Motion — Chapter Practice, Grade 8

Problem 1

A runner covers 100 meters in 20 seconds. What is the average speed?

Answer and explanation

5 m/s

Speed = distance ÷ time = 100 ÷ 20 = 5 m/s.

Problem 2

A train travels 300 km in 4 hours. What is its average speed?

Answer and explanation

75 km/h

Speed = distance ÷ time = 300 ÷ 4 = 75 km/h.

Problem 3

A skateboarder speeds up from 2 m/s to 8 m/s in 3 seconds. Find the acceleration.

Answer and explanation

2 m/s²

Acceleration = (8 − 2) ÷ 3 = 6 ÷ 3 = 2 m/s².

Problem 4

Which quantity includes BOTH speed and direction?

distance
velocity
time
mass

Answer and explanation

velocity

Velocity is speed given with a direction.

Problem 5

Explain the difference between speed and velocity using an example.

Answer and explanation

Speed only tells you how fast something is moving, like 50 km/h. Velocity tells you how fast AND in what direction, like 50 km/h north. Two cars traveling the same speed in opposite directions have the same speed but different velocities.

Problem 6

A car slows from 30 m/s to 10 m/s in 4 seconds. What is its acceleration? (Include the correct sign.)

Answer and explanation

-5 m/s²

Acceleration = (10 − 30) ÷ 4 = −20 ÷ 4 = −5 m/s². The negative sign shows it's slowing down.

Problem 7

A student walks 30 m east then 30 m west in 40 s. Find average speed and average velocity. Explain the reasoning in your own words.

Answer and explanation

Average speed 1.5 m/s; average velocity 0 m/s.

Total distance=60 m; speed=60/40=1.5 m/s.

Displacement=0 m; average velocity=0/40=0 m/s.

Response criteria

Use the stated conditions.
Show the evidence or calculation.
Explain the conclusion and any stated limitation.

Problem 8

A cyclist covers 180 m in 30 s. Calculate average speed. Show the reasoning, not just the conclusion.

Hints

Distance counts the whole path; displacement compares endpoints.

Answer and explanation

180/30=6 m/s.

Problem 9

Velocity changes from 2 m/s east to 10 m/s east in 4 s. Calculate average acceleration.

Hints

State what the supplied observations or conditions establish, and separate that from any assumption.

Answer and explanation

(10−2)/4=2 m/s² east, assuming east is positive.

Problem 10

Right is positive. A cart changes velocity from −2 to −8 m/s in 3 s. Calculate average acceleration and explain whether it speeds up or slows down.

Answer and explanation

(−8−(−2))/3 = −2 m/s². It speeds up toward the left because speed rises from 2 to 8 m/s.

Subtract signed velocities before dividing.

Compare velocity direction with acceleration direction.

Response criteria

Calculate −2 m/s².
Explain leftward motion.
Reject negative-always-slows.

Problem 11

The path covers 30 m east and 10 m west, for 40 m distance and 20 m east displacement. Arrows separate the journey from the start-to-finish comparison. The schematic horizontal positions are not a precision scale and do not establish a changing speed without elapsed-time data.

For this unit’s illustrated case, how can a trip have zero displacement without zero distance?

Answer and explanation

The final position can equal the initial position even after a nonzero path. Displacement uses endpoints; distance adds the traveled path.

A student walks 6 m east and 6 m west back to the start. Distance is 12 m; displacement is zero. Mark the route and endpoints separately so the calculation answers the intended question.

The final position can equal the initial position even after a nonzero path. Displacement uses endpoints; distance adds the traveled path.

Response criteria

Use the named labels, directions or supplied quantities accurately.
Connect the visual evidence to the scientific mechanism or calculation.
State the relevant model conditions or limitation.

Problem 12

Right is positive. A cart’s velocity changes from −3 to −9 m/s in 2 s. Find average acceleration and explain its speed change.

Answer and explanation

Average acceleration = (−9−(−3))/2 = −3 m/s²; speed increases leftward from 3 to 9 m/s. Negative acceleration does not always mean slowing.

Subtract signed velocities.

Compare the magnitudes and directions instead of using a sign slogan.

Average acceleration = (−9−(−3))/2 = −3 m/s²; speed increases leftward from 3 to 9 m/s. Negative acceleration does not always mean slowing.

Response criteria

Use the named labels, directions or supplied quantities accurately.
Connect the visual evidence to the scientific mechanism or calculation.
State the relevant model conditions or limitation.

Problem 13

A horizontal position–time segment means…

rest
constant positive acceleration
infinite speed
motion backward

Answer and explanation

rest

Position does not change.

Problem 14

Position changes from 3 m to 15 m in 4 s. Find average velocity.

Answer and explanation

3 m/s

(15 − 3) ÷ 4 = 3.

Problem 15

Does a falling position–time line always mean slowing down?

Answer and explanation

No. It means position decreases. A straight falling line represents constant negative velocity.

Problem 16

Position changes from 4 m at 2 s to 16 m at 6 s on a straight segment. Find its velocity. Explain the reasoning in your own words.

Answer and explanation

Constant velocity of +3 m/s over this segment.

Vertical change=16−4=12 m; time change=6−2=4 s.

Slope=12/4=3 m/s.

Response criteria

Use the stated conditions.
Show the evidence or calculation.
Explain the conclusion and any stated limitation.

Problem 17

A straight position–time segment goes from 12 m at 1 s to 4 m at 5 s. Find its velocity. Show the reasoning, not just the conclusion.

Hints

Read slope, not the vertical height, as velocity on a position–time graph.

Answer and explanation

(4−12)/(5−1)=−2 m/s; negative indicates motion toward decreasing position.

Problem 18

Can a position–time graph tell you the road's hills directly? Explain.

Hints

State what the supplied observations or conditions establish, and separate that from any assumption.

Answer and explanation

No. The vertical axis is position along a chosen coordinate, not necessarily road elevation. Interpret the labeled axes.

Problem 19

Does the final downward line prove decreasing speed?

Answer and explanation

No. A straight downward position line has constant negative velocity in the simplified interval. Its direction differs from its speed magnitude.

Response criteria

Use the supplied conditions and relevant evidence.
Explain the scientific mechanism or calculation.
State a meaningful limitation or testable next step.

Problem 20

Supplied positions at 0, 2, 4 and 6 s are 0, 6, 6 and 2 m, with right positive. The graph connects these recorded points. Find average velocity for each interval and explain the difference between a level position graph and a level nonzero velocity graph.

Answer and explanation

The interval velocities are +3, 0 and −2 m/s. A level position graph means unchanged location; a level nonzero velocity graph means steady motion. The axes determine the interpretation. Straight segments describe the simplified interval model rather than measurements at every possible instant.

Response criteria

Use the supplied conditions and relevant evidence.
Explain the scientific mechanism or calculation.
State a meaningful limitation or testable next step.

Problem 21

Read the supplied +3 m/s then −2 m/s graph, each interval lasting 2 s. Calculate distance, displacement and average speed.

Answer and explanation

Distance 10 m; displacement +2 m; average speed 2.5 m/s.

Compute signed areas +6 and −4 m.

Add magnitudes for distance and divide by 4 s for average speed.

Response criteria

Use signed area for displacement.
Use magnitudes for distance.
State average-speed units.

Problem 22

Position is measured as 0 m at 0 s and 4 m at 2 s. Does this prove constant 2 m/s velocity? Use the straight and curved proposals to suggest a test.

Answer and explanation

No. It establishes average velocity 2 m/s. The straight proposal predicts 2 m at 1 s and the curved proposal 1 m; an intermediate measurement can distinguish them.

Compare two models fitting the same endpoints.

Use a discriminating intermediate prediction.

Response criteria

Distinguish average from constant velocity.
Supply both intermediate predictions.
Propose an actual measurement.

Problem 23

Recorded positions give interval slopes +3, 0 and −2 m/s. A horizontal position segment means unchanged position, while a downward segment means a negative velocity under the chosen positive direction. Straight connections are a simplified interval model, not a record at every intermediate instant.

For this unit’s illustrated case, what does a horizontal position-time section show?

Answer and explanation

Position remains unchanged during that interval, so the object is at rest relative to the chosen reference, provided the graph accurately represents the motion.

A graph rising from position 0 m to 6 m over 3 s describes increasing position. It does not mean an object physically climbed a diagonal track. Write a sentence explaining each axis before describing motion.

Position remains unchanged during that interval, so the object is at rest relative to the chosen reference, provided the graph accurately represents the motion.

Response criteria

Use the named labels, directions or supplied quantities accurately.
Connect the visual evidence to the scientific mechanism or calculation.
State the relevant model conditions or limitation.

Problem 24

A velocity–time record is +4 m/s for 3 s followed by −1 m/s for 2 s. Calculate distance, displacement and average velocity over the full five seconds.

Answer and explanation

Distance 12+2 = 14 m; displacement 12−2 = 10 m right; average velocity 10/5 = 2 m/s right.

Use signed rectangle areas for displacement.

Add path magnitudes for distance and divide displacement by total time for average velocity.

Distance 12+2 = 14 m; displacement 12−2 = 10 m right; average velocity 10/5 = 2 m/s right.

Response criteria

Use the named labels, directions or supplied quantities accurately.
Connect the visual evidence to the scientific mechanism or calculation.
State the relevant model conditions or limitation.

Problem 25

A 10 kg object experiences a net force of 50 N. What is its acceleration?

Answer and explanation

5 m/s²

a = F ÷ m = 50 ÷ 10 = 5 m/s².

Problem 26

What net force is needed to accelerate a 2 kg ball at 6 m/s²?

Answer and explanation

12 N

F = ma = 2 × 6 = 12 N.

Problem 27

A 1,500 kg car accelerates at 2 m/s². What net force does the engine provide?

Answer and explanation

3000 N

F = ma = 1,500 × 2 = 3,000 N.

Problem 28

An astronaut floating in deep space, far from any forces, will…

slowly stop on her own
continue moving at constant velocity forever
accelerate away with no cause
spin uncontrollably

Answer and explanation

continue moving at constant velocity forever

With no unbalanced force acting on her, Newton's first law says her velocity won't change.

Problem 29

When a swimmer pushes backward on the water, the water pushes the swimmer forward. This illustrates Newton's…

first law
second law
third law
law of gravity

Answer and explanation

third law

This is an action-reaction pair, which is Newton's third law.

Problem 30

A rocket's engines produce 12,000 N of thrust, accelerating it at 4 m/s². What is the rocket's mass?

Answer and explanation

3000 kg

m = F ÷ a = 12,000 ÷ 4 = 3,000 kg.

Problem 31

A net horizontal force of 12 N acts on a 4 kg cart. Calculate acceleration and identify the reaction to a hand's push. Explain the reasoning in your own words.

Answer and explanation

3 m/s² in the net-force direction; the cart exerts an equal opposite force on the hand.

Acceleration=Fnet/m=12/4=3 m/s².

The reaction to the hand pushing the cart is the cart pushing the hand, on a different object.

Response criteria

Use the stated conditions.
Show the evidence or calculation.
Explain the conclusion and any stated limitation.

Problem 32

Net force 20 N acts on a 5 kg object. Find acceleration. Show the reasoning, not just the conclusion.

Hints

Use net force on one object in Newton's second law.

Answer and explanation

20/5=4 m/s² in the net-force direction.

Problem 33

A passenger lurches forward when a bus brakes. Explain without inventing a new forward force.

Hints

State what the supplied observations or conditions establish, and separate that from any assumption.

Answer and explanation

The passenger's body tends to maintain its forward velocity; a restraint or contact must exert a backward force to slow it.

Problem 34

Plan two comparisons from the records: one isolating net force, the other mass. Specify motion measurements, repeats, controls and what outcome would challenge the predicted relation. Explain braking separately from velocity direction.

Hints

Use the illustrated study titled Investigate force and mass separately. Keep the observations, model and conditions separate.

Answer and explanation

Compare the 1 kg cases at 1 and 2 N to isolate net force; compare 1, 2 and 4 kg at 2 N to isolate mass. Match path, resisting conditions, timing, measuring procedure and initial state. Keep all repeated records. The supplied model gives a=Fnet/m; unexpected motion needs a boundary/force/method review rather than automatic rejection of conservation or hidden invented values. A leftward net force can slow rightward motion.

Response criteria

Design two separately controlled comparisons.
Specify recorded motion, units and repeats.
Explain a challenge result and braking mechanism.

Problem 35

The cart diagram shows 10 N right and 4 N left on a 2 kg cart. A student calculates 5 m/s² using the push alone. Correct the method and say whether the cart must currently move right.

Answer and explanation

Net force is 6 N right; acceleration is 3 m/s² right. The current velocity is not given: the cart could be moving left and slowing.

Subtract resistance from the applied push.

Divide net force by mass.

Keep acceleration distinct from current motion.

Response criteria

Calculate 6 N and 3 m/s².
Do not count the green net arrow again.
Avoid inferring current velocity.

Problem 36

Equal-time snapshots can show no position change or equal changes in position. Both are consistent with zero net force in an inertial reference frame. The moving cart does not need a forward net force to keep its constant velocity. On a real surface, rolling resistance can slow it unless balanced. The rest snapshots overlap intentionally; no extra force called inertia should be drawn.

For this unit’s illustrated case, why is inertia not an extra force on a force diagram?

Answer and explanation

Inertia describes how mass resists acceleration. It is not an interaction from another object and should not be added as a force arrow.

A released toy cart slows due to interactions such as rolling resistance, not because motion uses up a stored force. A passenger’s motion changes when a seat or restraint exerts force; connect the law to interactions rather than calling inertia a pushing force.

Inertia describes how mass resists acceleration. It is not an interaction from another object and should not be added as a force arrow.

Response criteria

Use the named labels, directions or supplied quantities accurately.
Connect the visual evidence to the scientific mechanism or calculation.
State the relevant model conditions or limitation.

Problem 37

A 2.5 kg cart has a 15 N applied push and 5 N resistance. Find acceleration, and explain why its equal force on the pusher does not cancel that acceleration.

Answer and explanation

Net force is 10 N in the push direction and acceleration 10/2.5 = 4 m/s². The cart-on-pusher partner acts on the pusher, so it is not part of the cart’s net force.

Compute net force before dividing by mass.

Name the receiver of each interaction partner.

Net force is 10 N in the push direction and acceleration 10/2.5 = 4 m/s². The cart-on-pusher partner acts on the pusher, so it is not part of the cart’s net force.

Response criteria

Use the named labels, directions or supplied quantities accurately.
Connect the visual evidence to the scientific mechanism or calculation.
State the relevant model conditions or limitation.

Problem 38

Why is an afterward photograph insufficient to detect temporary deformation?

Answer and explanation

An object can deform during contact and then recover. The after-image does not show the complete time sequence.

Response criteria

Use the supplied conditions and relevant evidence.
Explain the scientific mechanism or calculation.
State a meaningful limitation or testable next step.

Problem 39

Does greater acceleration of the lighter cart imply a larger collision force on it?

Answer and explanation

No. Equal interaction forces can cause different acceleration because masses differ, and net-force calculations must account for other forces.

Response criteria

Use the supplied conditions and relevant evidence.
Explain the scientific mechanism or calculation.
State a meaningful limitation or testable next step.

Problem 40

Can speed alone predict every dent?

Answer and explanation

No. It influences motion energy, but material response, geometry and how the object stops also affect damage.

Response criteria

Use the supplied conditions and relevant evidence.
Explain the scientific mechanism or calculation.
State a meaningful limitation or testable next step.

Problem 41

What do these peak records support?

Answer and explanation

Lower measured peak force for this padded setup under the stated matched conditions. They do not certify every pad or establish identical average forces or injury protection.

Response criteria

Use the supplied conditions and relevant evidence.
Explain the scientific mechanism or calculation.
State a meaningful limitation or testable next step.

Problem 42

Illustrative matched-cart tests show bumper thickness 15 mm before, 8 mm during and 15 mm afterward; peak force is 12 N rather than 24 N for a rigid stop. Explain the temporary deformation and compare peak values without declaring all collisions safe.

Answer and explanation

The bumper undergoes elastic deformation in this simplified record because it regains its thickness. The padded peak is half the rigid-stop peak under matched conditions. Deformation can allow a longer stopping interval, but the readings do not prove that every object is protected or give the entire force–time history. Energy is redistributed rather than erased.

Response criteria

Use the supplied conditions and relevant evidence.
Explain the scientific mechanism or calculation.
State a meaningful limitation or testable next step.

Problem 43

Two collisions have the same initial kinetic energy but different damage. Is energy conservation violated?

Answer and explanation

No. Different materials and stopping conditions can distribute the energy differently. Conservation does not require the same peak force, deformation or damage.

Response criteria

Use the supplied conditions and relevant evidence.
Explain the scientific mechanism or calculation.
State a meaningful limitation or testable next step.

Problem 44

Evaluate and correct: A recovered bumper never changed shape.

Answer and explanation

It may have changed temporarily during contact; use a before–during–after record.

Response criteria

Use the supplied conditions and relevant evidence.
Explain the scientific mechanism or calculation.
State a meaningful limitation or testable next step.

Problem 45

Choose one prediction from this unit. Explain a comparison that could test it, specifying observations, changed and matched conditions, and a result that would challenge it.

Answer and explanation

Illustrative tests for matched carts at the same speed show peak readings of 18, 19, 20 N without padding and 9, 10, 11 N with padding. Check repeated trials, measuring method and pad thickness before generalizing to other objects. Lower measured peak force for this padded setup under the stated matched conditions. They do not certify every pad or establish identical average forces or injury protection.

Response criteria

Use the supplied conditions and relevant evidence.
Explain the scientific mechanism or calculation.
State a meaningful limitation or testable next step.

Problem 46

A bumper is 12 mm thick before contact, 7 mm during and 11 mm after. Explain what the record supports about temporary and remaining deformation and what it cannot establish about force.

Hints

Distinguish the observed quantities, the proposed mechanism and its conditions.

Answer and explanation

It compresses 5 mm temporarily and retains a 1 mm thickness change after the recorded interaction. It does not fully recover in that record. Thickness alone does not establish a peak force or permanent behavior over all later times; a suitable force/time record and longer observation are needed.

Problem 47

Two collisions have the same initial kinetic energy but different damage. Is energy conservation violated? Explain a condition that would change this conclusion.

Hints

Distinguish the observed quantities, the proposed mechanism and its conditions.

Answer and explanation

No. Different materials and stopping conditions can distribute the energy differently. Conservation does not require the same peak force, deformation or damage.

Problem 48

These equal-mass carts illustrate an ideal one-dimensional elastic collision: the initially moving cart can stop while the initially stationary cart moves. Interaction-force arrows apply during contact, while velocity arrows describe motion before or after. The snapshots omit detailed deformation and other forces and do not claim that all real collisions exchange velocities or conserve mechanical kinetic energy.

For this unit’s illustrated case, why should the contact-force arrows not be carried into the separated after-collision snapshot?

Answer and explanation

The contact interaction has ended once the carts separate. A remaining velocity is not evidence of a continuing contact push; other real interactions must be named separately.

A timeline is important because different interactions exist at different stages. An elastic collision is an ideal case where the system’s kinetic energy is retained after separation. A damaged or thermally dissipative collision can have a different outcome.

The contact interaction has ended once the carts separate. A remaining velocity is not evidence of a continuing contact push; other real interactions must be named separately.

Response criteria

Use the named labels, directions or supplied quantities accurately.
Connect the visual evidence to the scientific mechanism or calculation.
State the relevant model conditions or limitation.

Problem 49

Two carts receive equal opposite 12 N contact forces in a stated horizontal interval. Their masses are 3 and 1.5 kg. Compare accelerations and explain whether equal force means equal velocity change over the same duration.

Answer and explanation

Accelerations are 4 and 8 m/s² in opposite directions. Over the same duration the lighter cart’s velocity change has twice the magnitude, despite the equal force pair.

Use each receiver’s mass in Fnet/m under the supplied net-horizontal-force assumption.

Multiply acceleration by the common interval to compare velocity changes.

Accelerations are 4 and 8 m/s² in opposite directions. Over the same duration the lighter cart’s velocity change has twice the magnitude, despite the equal force pair.

Response criteria

Use the named labels, directions or supplied quantities accurately.
Connect the visual evidence to the scientific mechanism or calculation.
State the relevant model conditions or limitation.

Problem 50

Why define the dent measure before seeing results?

Answer and explanation

A fixed rule allows consistent judgments and avoids changing success criteria to favor a preferred design.

Response criteria

Use the supplied conditions and relevant evidence.
Explain the scientific mechanism or calculation.
State a meaningful limitation or testable next step.

Problem 51

Does a larger contact face automatically mean a smaller total force?

Answer and explanation

No. It can lower pressure for the same force by spreading contact area, but total force depends on the stopping interaction.

Response criteria

Use the supplied conditions and relevant evidence.
Explain the scientific mechanism or calculation.
State a meaningful limitation or testable next step.

Problem 52

Why is B’s single 10 N reading an incomplete comparison?

Answer and explanation

It omits its other readings and variability. Evaluate all planned trials along with constraints and damage observations.

Response criteria

Use the supplied conditions and relevant evidence.
Explain the scientific mechanism or calculation.
State a meaningful limitation or testable next step.

Problem 53

Does combining useful features prove the new protector is better?

Answer and explanation

No. Features can interact and violate limits. The revised design requires new tests under the same evaluation rules.

Response criteria

Use the supplied conditions and relevant evidence.
Explain the scientific mechanism or calculation.
State a meaningful limitation or testable next step.

Problem 54

Illustrative designs have A: mean peak 13 N, thickness 4 cm; B: mean peak 9 N, thickness 7 cm. Maximum permitted thickness is 5 cm. Choose a qualifying starting design and propose an evidence-based revision.

Answer and explanation

A qualifies under the thickness rule; B does not despite its lower mean peak. Start with A and investigate whether a more compressible arrangement within 5 cm lowers the peak. Repeat matched tests, record all results and evaluate permanent deformation as well as force. Lower mean peak alone is not universal protection.

Response criteria

Use the supplied conditions and relevant evidence.
Explain the scientific mechanism or calculation.
State a meaningful limitation or testable next step.

Problem 55

A revised case protects one trial but fails two. Can its successful trial justify calling it reliable?

Answer and explanation

No. All planned trials matter. Report the failures, investigate their causes, and revise the design or the limited claim rather than selecting only the success.

Response criteria

Use the supplied conditions and relevant evidence.
Explain the scientific mechanism or calculation.
State a meaningful limitation or testable next step.

Problem 56

Evaluate and correct: The design with the lowest one-trial reading is always best.

Answer and explanation

Judge repeated evidence, variability, damage measures and hard constraints, rather than one selected reading.

Response criteria

Use the supplied conditions and relevant evidence.
Explain the scientific mechanism or calculation.
State a meaningful limitation or testable next step.

Problem 57

Choose one prediction from this unit. Explain a comparison that could test it, specifying observations, changed and matched conditions, and a result that would challenge it.

Answer and explanation

Combine A’s stable arrangement with B’s more compressible layer if the size and mass limits allow it. Predict reduced typical peak while retaining consistency, then collect new data. The combination is a proposal until tested. No. Features can interact and violate limits. The revised design requires new tests under the same evaluation rules.

Response criteria

Use the supplied conditions and relevant evidence.
Explain the scientific mechanism or calculation.
State a meaningful limitation or testable next step.

Problem 58

Protector C gives repeated peaks 11, 17 and 14 N within the allowed thickness. Calculate mean and range and explain why the single lowest trial is insufficient.

Hints

Distinguish the observed quantities, the proposed mechanism and its conditions.

Answer and explanation

Mean is 14 N and range 6 N. The 11 N minimum omits the other trials and understates variability. Compare all planned results with criteria, constraints and damage observations before choosing or revising.

Problem 59

A revised case protects one trial but fails two. Can its successful trial justify calling it reliable? Explain a condition that would change this conclusion.

Hints

Distinguish the observed quantities, the proposed mechanism and its conditions.

Answer and explanation

No. All planned trials matter. Report the failures, investigate their causes, and revise the design or the limited claim rather than selecting only the success.

Problem 60

The comparison proposes that a compressible ring arrangement provides more deformation travel than a very thin pad under a matched test load. Geometry is shown schematically, and no measured force reduction is supplied by this drawing. A protector must still be checked for stability, maximum compression, size and repeat performance; adding material without a mechanism is not enough.

For this unit’s illustrated case, which measurement could distinguish “more travel” from “a prettier design”?

Answer and explanation

Measure deformation or stopping distance/time under matched loads and then evaluate peak-force/damage criteria using an appropriate safe test or supplied records.

A mechanism explains how the feature changes the interaction. OpenSciEd’s ring sketches below give concrete shapes to compare, but an unloaded drawing cannot establish their performance. Predict, test, revise and retest.

Measure deformation or stopping distance/time under matched loads and then evaluate peak-force/damage criteria using an appropriate safe test or supplied records.

Response criteria

Use the named labels, directions or supplied quantities accurately.
Connect the visual evidence to the scientific mechanism or calculation.
State the relevant model conditions or limitation.

Problem 61

A design must stay below 30 N in every trial. Its supplied results are 22, 24 and 35 N. Does a mean of 27 N establish that it meets the criterion? Explain a proper next step.

Answer and explanation

No. The 35 N trial fails the every-trial limit even though the mean is 27 N. Preserve the result, investigate variation, revise a mechanism and retest under matched conditions.

Read the criterion as every trial, not the mean.

Use all records before recommending a tested revision.

No. The 35 N trial fails the every-trial limit even though the mean is 27 N. Preserve the result, investigate variation, revise a mechanism and retest under matched conditions.

Response criteria

Use the named labels, directions or supplied quantities accurately.
Connect the visual evidence to the scientific mechanism or calculation.
State the relevant model conditions or limitation.