Conservation of Linear Momentum — IISER Physics MCQs with Solutions
Free IISER Physics Conservation of Linear Momentum 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 — Conservation of Linear Momentum · easy · theory
The total linear momentum of a system is conserved when:
A. Gravity is absent
B. The bodies are rigid
C. Kinetic energy is conserved
D. The net external force on the system is zero ✓ Correct
Solution: dP⃗/dt = F⃗_ext; zero net external force ⇒ P⃗ constant, whatever the internal forces (collisions, explosions).
Q2 — Conservation of Linear Momentum · medium · theory
A bomb at rest explodes into fragments. Immediately afterwards, the vector sum of the momenta of all fragments is:
A. Zero ✓ Correct
B. Random
C. Equal to the energy released
D. Directed upward
Solution: The explosion is internal: total momentum stays what it was — zero. (Kinetic energy, of course, increases.)
Q3 — Conservation of Linear Momentum · easy · numerical
A 40 kg boy on frictionless ice throws a 2 kg ball at 10 m/s. His recoil speed is:
A. 0.5 m/s ✓ Correct
B. 0.05 m/s
C. 5 m/s
D. 2 m/s
Solution: 40v = 2×10 ⇒ v = 0.5 m/s backwards.
Q4 — Conservation of Linear Momentum · medium · numerical
A 10 g bullet is fired at 500 m/s from a 5 kg rifle. The rifle's recoil speed is:
A. 0.1 m/s
B. 1 m/s ✓ Correct
C. 2 m/s
D. 10 m/s
Solution: v = (0.01×500)/5 = 1 m/s. The rifle's KE is far smaller — momentum is shared equally, energy is not.
Q5 — Conservation of Linear Momentum · hard · numerical
A shell at rest explodes into two pieces with mass ratio 1 : 3. The ratio of their kinetic energies (light : heavy) is:
A. 9 : 1
B. 1 : 3
C. 3 : 1 ✓ Correct
D. 1 : 1
Solution: Equal/opposite momenta ⇒ KE = p²/2m ∝ 1/m ⇒ 3:1 — the lighter piece takes the lion's share of energy.
Q6 — Conservation of Linear Momentum · medium · numerical
A 60 kg man jumps with velocity 4 m/s from a stationary 240 kg trolley (free to roll). The trolley recoils at:
A. 1 m/s ✓ Correct
B. 4 m/s
C. 0.5 m/s
D. 2 m/s
Solution: 240v = 60×4 ⇒ v = 1 m/s opposite the jump.
Q7 — Conservation of Linear Momentum · hard · theory
Momentum conservation in an explosion holds even though mechanical energy is NOT conserved because:
A. Energy conservation implies momentum conservation
B. The explosion is elastic
C. The fragments are massless
D. Momentum depends only on the absence of external forces, while chemical energy converts to KE internally ✓ Correct
Solution: The two laws are independent: internal forces cannot change P⃗ (Newton III), but internal energy release CAN change total KE.
Q8 — Conservation of Linear Momentum · hard · numerical
A 3 kg shell at rest explodes into three 1 kg pieces. Two fly at 4 m/s each at right angles to each other. The speed of the third piece is:
A. 8 m/s
B. 4 m/s
C. 2√2 m/s
D. 4√2 ≈ 5.7 m/s ✓ Correct
Solution: Resultant of the two = √(16+16) = 4√2; the third must cancel it: v = 4√2 ≈ 5.7 m/s opposite the diagonal.