AP Physics Physics: Classical Mechanics & Kinematics 5 — Questions and Answers
Question 1: A ball is thrown horizontally at 10 m/s from a cliff. After 2 s, what is the ball's vertical velocity component? (g = 10 m/s²)
- 10 m/s downward
- 20 m/s downward (Correct answer)
- 10 m/s upward
- 20 m/s upward
Correct answer: 20 m/s downward
Vertical velocity = gt = 10 × 2 = 20 m/s downward (horizontal launch means initial vertical velocity is zero).
Question 2: Which of the following is an example of a non-inertial reference frame?
- A train moving at constant velocity on straight tracks
- A car accelerating from a stoplight (Correct answer)
- A ship sailing at constant speed in a straight line
- A stationary room on Earth's surface
Correct answer: A car accelerating from a stoplight
An accelerating car is a non-inertial frame because Newton's first law does not hold without introducing pseudo-forces.
Question 3: A block of mass 4 kg sits on a surface with μs = 0.5. What is the minimum horizontal force needed to start the block moving? (g = 10 m/s²)
- 5 N
- 10 N
- 20 N (Correct answer)
- 40 N
Correct answer: 20 N
Maximum static friction = μs × mg = 0.5 × 4 × 10 = 20 N; the applied force must exceed this to start motion.
Question 4: A sprinter starting from rest reaches 9 m/s in 3 s. What is the sprinter's average acceleration?
- 1 m/s²
- 3 m/s² (Correct answer)
- 6 m/s²
- 27 m/s²
Correct answer: 3 m/s²
Average acceleration = Δv/Δt = (9 − 0)/3 = 3 m/s².
Question 5: Two vectors A = 3 m East and B = 4 m North are added. What is the direction of the resultant vector relative to East?
- 37° North of East
- 53° North of East (Correct answer)
- 37° East of North
- 45° North of East
Correct answer: 53° North of East
θ = arctan(4/3) ≈ 53° North of East; the larger northward component makes the angle closer to North.
Question 6: Which scenario correctly illustrates the concept of relative velocity?
- A ball dropped in a moving train lands directly below the release point as seen by a ground observer
- A passenger walks forward at 2 m/s on a train moving at 10 m/s; a ground observer sees them move at 12 m/s (Correct answer)
- An object at rest has velocity relative to all frames of reference
- Two cars moving in opposite directions at 30 m/s each have a relative velocity of 30 m/s
Correct answer: A passenger walks forward at 2 m/s on a train moving at 10 m/s; a ground observer sees them move at 12 m/s
Velocities add when moving in the same direction: v_ground = v_train + v_passenger = 10 + 2 = 12 m/s.
Question 7: A car travels 60 km north, then 80 km east. What is the magnitude of its displacement from the starting point?
- 100 km (Correct answer)
- 120 km
- 140 km
- 160 km
Correct answer: 100 km
Displacement = √(60² + 80²) = √(3600 + 6400) = √10000 = 100 km.
AP Physics Physics: Classical Mechanics & Kinematics 5
A ball is thrown horizontally at 10 m/s from a cliff.
After 2 s, what is the ball's vertical velocity component? (g = 10 m/s²)