AP Physics Physics: Momentum, Impulse & Collisions 1 — Questions and Answers
Question 1: What is the momentum of a 5 kg object moving at 10 m/s?
- 2 kg·m/s
- 15 kg·m/s
- 50 kg·m/s (Correct answer)
- 0.5 kg·m/s
Correct answer: 50 kg·m/s
Momentum p = mv = 5 kg × 10 m/s = 50 kg·m/s.
Question 2: The impulse-momentum theorem states that the net impulse on an object equals:
- The change in kinetic energy
- The change in momentum (Correct answer)
- The net force times distance
- The work done on the object
Correct answer: The change in momentum
The impulse-momentum theorem states J = Δp, meaning impulse equals the change in momentum.
Question 3: A net force of 100 N acts on a 0.5 kg ball for 0.05 s. What is the magnitude of the impulse?
- 2,000 N·s
- 0.5 N·s
- 5 N·s (Correct answer)
- 50 N·s
Correct answer: 5 N·s
Impulse J = FΔt = 100 N × 0.05 s = 5 N·s.
Question 4: Which of the following is a vector quantity?
- Speed
- Kinetic energy
- Momentum (Correct answer)
- Mass
Correct answer: Momentum
Momentum p = mv is a vector because it has both magnitude and direction, following the direction of velocity.
Question 5: A 2 kg object increases its velocity from 3 m/s to 7 m/s. What impulse was applied?
- 20 N·s
- 8 N·s (Correct answer)
- 4 N·s
- 14 N·s
Correct answer: 8 N·s
Impulse J = mΔv = 2 kg × (7 − 3) m/s = 8 N·s.
Question 6: Why do airbags reduce injury in car crashes?
- They increase the force of impact
- They decrease the total change in momentum
- They increase the time over which the impulse acts, reducing the average force (Correct answer)
- They convert all kinetic energy into heat
Correct answer: They increase the time over which the impulse acts, reducing the average force
Since J = FΔt = Δp, a longer collision time Δt means a smaller average force F for the same impulse, reducing injury.
Question 7: A net force of 20 N acts on a 4 kg object for 3 seconds. What is the resulting change in velocity?
- 5 m/s
- 15 m/s (Correct answer)
- 60 m/s
- 0.27 m/s
Correct answer: 15 m/s
J = FΔt = 20 × 3 = 60 N·s; Δv = J/m = 60/4 = 15 m/s.
AP Physics Physics: Momentum, Impulse & Collisions 1
What is the momentum of a 5 kg object moving at 10 m/s?