Velocity & Acceleration — Practice · Grade 12 Science
Chapter: Motion & KinematicsWhat this practice 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.
10 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
Answer and explanation
8 m/s
Average velocity = displacement ÷ time = 100 ÷ 12.5 = 8 m/s.
Problem 2
Answer and explanation
3 m/s²
a = (v − v₀) ÷ t = (22 − 10) ÷ 4 = 12 ÷ 4 = 3 m/s².
Problem 3
- 0 m/s², since it is momentarily at rest
- 9.8 m/s² directed downward
- 9.8 m/s² directed upward
- It cannot be determined
Answer and explanation
9.8 m/s² directed downward
Gravity acts the whole time, so the acceleration stays 9.8 m/s² downward even when the velocity is instantaneously zero.
Problem 4
Answer and explanation
49 m/s
v = v₀ + gt = 0 + 9.8 × 5.0 = 49 m/s.
Problem 5
Answer and explanation
-8 m/s²
a = (v − v₀) ÷ t = (4 − 28) ÷ 3 = −24 ÷ 3 = −8 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
Answer and explanation
Average velocity is the total displacement divided by the total time for the whole trip — it smooths everything into one number, like driving 270 km north in 3 hours for an average velocity of 90 km/h north. Instantaneous velocity is how fast (and which way) you are moving at one specific moment, like the 120 km/h your speedometer reads on the open highway or the 0 km/h at a rest stop. The average can hide big swings in the instantaneous value.
Problem 7
Hints
Acceleration sign alone does not say whether speed increases.
Answer and explanation
(15−3)/4=3 m/s².
Problem 8
Hints
State what the supplied observations or conditions establish, and separate that from any assumption.
Answer and explanation
Yes. A return trip has zero displacement but nonzero traveled distance.
Problem 9
Answer and explanation
Yes. The endpoint average is still +2 m/s², while instantaneous acceleration could vary.
Average acceleration is Δv/Δt, so the numerator is final velocity minus initial velocity with signs retained. Here the change from −3 to +5 m/s is +8 m/s over 4 s, giving +2 m/s². This average does not by itself prove acceleration was constant within the interval. The units mean a velocity change of meters per second for every second, not a distance traveled per second squared.
Yes. The endpoint average is still +2 m/s², while instantaneous acceleration could vary.
Response criteria
- Interpret labels, structures, axes, units and directions correctly.
- Explain the physical or environmental relationship or mechanism.
- Respect stated assumptions and distinguish observation from inference.
Problem 10
Answer and explanation
a=(−4−8)/6=−2 m/s². v=0 at 4 s. Displacement=8×6+½(−2)×6²=12 m; positive net displacement does not mean it moved east for the entire interval.
a=(−4−8)/6=−2 m/s². v=0 at 4 s.
Displacement=8×6+½(−2)×6²=12 m; positive net displacement does not mean it moved east for the entire interval.
Response criteria
- Use the stated measurements or conditions, with correct units.
- Connect the result to the physical or environmental mechanism or evidence relationship.
- Identify the assumption, model limit or further evidence requested.