Impulse & Impulse-Momentum Theorem — IISER Physics MCQs with Solutions
Free IISER Physics Impulse & Impulse-Momentum Theorem MCQs with step-by-step solutions (8 questions). Part of Centre of Mass, Momentum & Collisions. Practise online on Prepizo — no login needed.
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Questions with solutions
Q1 — Impulse & Impulse-Momentum Theorem · easy · theory
Impulse of a force equals:
A. The change in kinetic energy
B. Force × displacement
C. Power × time
D. The change in momentum it produces (∫F dt = Δp) ✓ Correct
Solution: J⃗ = ∫F⃗dt = Δp⃗; its unit N·s ≡ kg·m/s. Graphically, the area under the F–t curve.
Q2 — Impulse & Impulse-Momentum Theorem · medium · theory
A cricketer draws his hands back while catching a fast ball. This reduces the force on his hands because:
A. The ball does less work
B. The ball's momentum change is reduced
C. The impulse becomes smaller
D. The same Δp is spread over a longer time, so F_avg = Δp/Δt drops ✓ Correct
Solution: Δp is fixed by the catch; lengthening Δt lowers the average force. Same physics as airbags and shock absorbers.
Q3 — Impulse & Impulse-Momentum Theorem · easy · numerical
A 0.15 kg cricket ball arrives at 20 m/s and is caught and stopped in 0.1 s. The average force on the hands is:
A. 3 N
B. 300 N
C. 15 N
D. 30 N ✓ Correct
Solution: F = Δp/Δt = 0.15×20/0.1 = 30 N.
Q4 — Impulse & Impulse-Momentum Theorem · medium · numerical
A 0.5 kg ball hits a wall normally at 12 m/s and rebounds at 8 m/s. The impulse on the ball is:
A. 10 N·s ✓ Correct
B. 4 N·s
C. 2 N·s
D. 6 N·s
Solution: Taking rebound positive: J = 0.5(8 − (−12)) = 0.5×20 = 10 N·s. Trap: speeds ADD when direction reverses.
Q5 — Impulse & Impulse-Momentum Theorem · hard · numerical
A force acting on a 2 kg body varies as a triangle on the F–t graph: rising 0→20 N over 0→2 s, falling to 0 at t = 4 s. The body starts at rest; its final speed is:
A. 10 m/s
B. 20 m/s ✓ Correct
C. 40 m/s
D. 80 m/s
Solution: Impulse = area = ½×4×20 = 40 N·s = mv ⇒ v = 20 m/s.
Q6 — Impulse & Impulse-Momentum Theorem · medium · numerical
A hammer of mass 1 kg moving at 10 m/s strikes a nail and stops in 0.01 s. The average force on the nail is:
A. 100 N
B. 1000 N ✓ Correct
C. 10 N
D. 10000 N
Solution: F = mv/t = 10/0.01 = 1000 N — why hammers work.
Q7 — Impulse & Impulse-Momentum Theorem · hard · theory
A ball bounces off a wall with no loss of speed. Even though kinetic energy is conserved in this collision, the wall must have exerted:
A. No force at all
B. An impulse equal to the ball's KE
C. Zero impulse
D. A large impulse (momentum was reversed) with negligible energy transfer ✓ Correct
Solution: Δp = 2mv is substantial, but the wall (effectively infinite mass) recoils with negligible speed, absorbing momentum yet almost no energy — impulse and energy transfer are distinct.
Q8 — Impulse & Impulse-Momentum Theorem · hard · numerical
A machine gun fires 10 g bullets at 500 m/s. If the gunner can sustain a maximum average force of 100 N, the maximum number of bullets he can fire per second is:
A. 5
B. 10
C. 50
D. 20 ✓ Correct
Solution: Each bullet needs Δp = 5 N·s of impulse. n × 5 ≤ 100 ⇒ n ≤ 20 bullets per second.