Velocity & Acceleration — Drills · Grade 12 Science

Chapter: Motion & Kinematics

What these drills covers

By the end of Velocity & Acceleration you should be able to:

I can distinguish average velocity, instantaneous velocity, and average speed, and calculate each.
I can define acceleration as the rate of change of velocity and calculate it, including its sign.
I can explain the meaning of g and apply it to objects in free fall.

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

Vocabulary used: average velocity, instantaneous velocity, average speed, acceleration, free fall, g.

Problem 1

A car's velocity increases from 4 m/s to 28 m/s in 6.0 s. Find its acceleration.

Answer and explanation

4 m/s²

a = (v − v₀) ÷ t = (28 − 4) ÷ 6 = 24 ÷ 6 = 4 m/s².

Problem 2

A ball is dropped from rest and falls freely for 2.0 s. How fast is it moving? (g = 9.8 m/s²)

Answer and explanation

19.6 m/s

v = v₀ + gt = 0 + 9.8 × 2.0 = 19.6 m/s.

Problem 3

A skater covers a 100 m displacement in 8.0 s. Find her average velocity.

Answer and explanation

12.5 m/s

Average velocity = displacement ÷ time = 100 ÷ 8.0 = 12.5 m/s.

Problem 4

Average velocity is calculated from which quantity divided by time?

acceleration
displacement
total distance
top speed

Answer and explanation

displacement

Average velocity uses displacement ÷ time, which is why a round trip back to the start has an average velocity of zero.

Problem 5

A car slows from 30 m/s to 6 m/s in 4.0 s. Find its acceleration, including the sign.

Answer and explanation

-6 m/s²

a = (6 − 30) ÷ 4 = −24 ÷ 4 = −6 m/s². Here the acceleration is opposite the stated positive velocity, so speed decreases during the interval. A negative acceleration does not mean slowing in every motion case.

Problem 6

A ball is thrown straight up. Explain why its acceleration is still 9.8 m/s² downward at the very top of its path, even though its velocity there is zero.

Answer and explanation

Gravity keeps acting on the ball for the entire flight, so it keeps changing the ball's velocity at 9.8 m/s² downward the whole time. At the top, the velocity is momentarily zero only because the ball has finished slowing down and is about to speed up downward — but the acceleration never pauses. Zero velocity and zero acceleration are completely different conditions.

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