Car A has mass 1000 kg moving at 20 m/s. Car B has mass 2000 kg moving at 10 m/s. Which has greater momentum magnitude?
ACar A, because it is faster
BCar B, because it is heavier
CThey are equal (both 20,000 kg·m/s)
DCannot be determined without direction information
Momentum = mv. Car A: 1000 × 20 = 20,000 kg·m/s. Car B: 2000 × 10 = 20,000 kg·m/s. They are equal. This illustrates that momentum balances mass and velocity linearly — unlike kinetic energy (½mv²), which would give Car A (KE = 200,000 J) twice the energy of Car B (KE = 100,000 J).
Question 2 True / False
A large impulse usually requires a large force acting over a long period of time.
TTrue
FFalse
Answer: False
Impulse is J = FΔt (or ∫F dt for variable force). A very large force acting over a very short time can deliver a large impulse — a golf club striking a ball involves milliseconds of contact but enormous force. What matters is the product FΔt, not either factor alone. This is also why airbags work: they increase Δt to reduce the peak force for the same total impulse.
Question 3 Short Answer
A 0.5 kg ball moving at 10 m/s strikes a wall and bounces back at 8 m/s in the opposite direction. What is the magnitude of the impulse delivered to the ball?
Think about your answer, then reveal below.
Model answer: 9 kg·m/s
Impulse = Δp = m(v_f − v_i). Taking the initial direction as positive: v_i = +10 m/s, v_f = −8 m/s. Δp = 0.5 × (−8 − 10) = 0.5 × (−18) = −9 kg·m/s. The magnitude is 9 kg·m/s. A common error is ignoring the direction reversal and computing 0.5 × (10 − 8) = 1 kg·m/s — but the sign change from the bounce is the whole story here.