Levers, Ramps & Pulleys — Practice · Grade 8 Science

Chapter: Work & Machines

What this practice covers

By the end of Levers, Ramps & Pulleys you should be able to:

10 questions, multiple choice and written answer, each with a worked explanation.

Vocabulary used: simple machine, fulcrum, ideal machine, model, evidence, system boundary, assumption.

Problem 1

A longer ramp to the same height usually trades…
  1. more force for less distance
  2. less force for more distance
  3. zero work for motion
  4. mass for energy
Answer and explanation

less force for more distance

The force acts over a longer distance.

Problem 2

A lever pivots around a…
  1. battery
  2. fulcrum
  3. magnetic pole
  4. wavelength
Answer and explanation

fulcrum

The fulcrum is its pivot.

Problem 3

Does a fixed pulley necessarily reduce the size of the force needed?
Answer and explanation

No. An ideal fixed pulley can redirect the force while leaving its size unchanged.

Problem 4

An ideal ramp raises a 60 N load by 0.5 m over a 3 m path. Find output work and ideal input force. Explain the reasoning in your own words.
Answer and explanation

30 J of output work and 10 N ideal effort, ignoring friction.

Output work=60×0.5=30 J.

Ideal input work is also 30 J; force=30/3=10 N.

Response criteria

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

Problem 5

An ideal pulley uses two supporting rope segments for a 60 N load. Find pulling force during a slow lift. Show the reasoning, not just the conclusion.
Hints

Both ideal methods transfer 100 J; the ramp does not create energy.

Answer and explanation

60/2=30 N, with the free end moving twice the load's distance.

Problem 6

Why does a real rough ramp require more than the ideal predicted force?
Hints

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

Answer and explanation

Friction transfers some input energy to thermal energy, so input work must exceed the load's gravitational-energy increase.

Problem 7

Why are these ramps not a scale drawing?
Answer and explanation

The drawn slopes and heights are arranged for readability. Use the stated 1 m, 2 m and 0.5 m dimensions for quantitative reasoning.

The drawn slopes and heights are arranged for readability. Use the stated 1 m, 2 m and 0.5 m dimensions for quantitative reasoning.

Response criteria

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

Problem 8

Illustrative ideal ramps raise the same load by 0.5 m. Ramp A is 1 m long and B 2 m long; measured input forces are 20 and 10 N under the simplified no-loss model. Compare input work and explain the force–distance trade-off. State why actual friction would change the required input.
Answer and explanation

Both have modeled input work 20 J: 20×1 and 10×2. The longer ramp reduces force while increasing travel distance for the same lift; it does not make energy. Actual friction can require greater input work and introduce thermal transfers. The simple along-ramp calculation uses the stated force direction and ideal model.

Both have modeled input work 20 J: 20×1 and 10×2. The longer ramp reduces force while increasing travel distance for the same lift; it does not make energy. Actual friction can require greater input work and introduce thermal transfers. The simple along-ramp calculation uses the stated force direction and ideal model.

Response criteria

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

Problem 9

A lever trades force against its distance from the pivotA lever trades force against its distance from the pivotEffort: 75 N downLoad on lever: 300 N downPivot support upArm: 4 m1 mTurning effects: 75×4 = 300×1. Forces shown act on the lever.
The ideal lever is balanced when the 75 N effort acts 4 m from the pivot and the 300 N load force acts 1 m from it. The turning effects match even though the forces differ. Both downward red arrows are forces on the lever; its upward force on the load is a different receiver’s force. Arrow lengths are qualitative here, while the arm distances and force labels supply the calculation.
For this unit’s illustrated case, why can the smaller effort balance the larger load force? Would moving the effort closer to the pivot keep the same balance?
Answer and explanation

Its arm is four times as long: 75×4 = 300×1. Moving the effort closer reduces its turning effect, so a larger effort would be needed under the same ideal conditions.

The pivot is the turning point. A force’s perpendicular distance from it affects turning. The lever does not create energy; during a small movement the long effort end travels farther than the short load end.

Its arm is four times as long: 75×4 = 300×1. Moving the effort closer reduces its turning effect, so a larger effort would be needed under the same ideal 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.

Problem 10

For an ideal balanced lever, the load exerts 180 N at an arm 0.2 m long. The effort arm is 0.6 m. Find the effort force and explain its distance tradeoff.
Answer and explanation

Effort is 180×0.2/0.6 = 60 N. The effort end travels about three times the load-end distance for the small-motion ideal comparison; the lever does not create energy.

Match turning effects F×arm on opposite sides.

Connect the 3:1 arm ratio to effort travel as well as force.

Effort is 180×0.2/0.6 = 60 N. The effort end travels about three times the load-end distance for the small-motion ideal comparison; the lever does not create energy.

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.

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