Inelastic & Perfectly Inelastic Collisions — JEE Main Physics MCQs with Solutions
Free JEE Main Physics Inelastic & Perfectly Inelastic Collisions 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 — Inelastic & Perfectly Inelastic Collisions · easy · theory
In a perfectly INELASTIC collision, the two bodies:
A. Stick together and move with a common velocity; KE is lost but momentum is conserved ✓ Correct
B. Exchange velocities
C. Conserve kinetic energy
D. Both stop always
Solution: Sticking = maximum possible KE loss consistent with momentum conservation. Momentum is still exactly conserved.
Q2 — Inelastic & Perfectly Inelastic Collisions · medium · theory
In ANY collision between two bodies (no external force), which is ALWAYS conserved?
A. Total kinetic energy
B. The velocity of the heavier body
C. Total linear momentum ✓ Correct
D. The speed of each body
Solution: Momentum conservation needs only F_ext = 0. KE survives only the elastic case — the single most-tested distinction.
Q3 — Inelastic & Perfectly Inelastic Collisions · easy · numerical
A 2 kg body at 6 m/s hits a 4 kg body at rest and sticks to it. Their common velocity is:
A. 3 m/s
B. 6 m/s
C. 1.5 m/s
D. 2 m/s ✓ Correct
Solution: v = 2×6/6 = 2 m/s.
Q4 — Inelastic & Perfectly Inelastic Collisions · medium · numerical
For that same collision (2 kg at 6 m/s onto 4 kg at rest, perfectly inelastic), the kinetic energy LOST is:
A. 12 J
B. 6 J
C. 36 J
D. 24 J ✓ Correct
Solution: KE_i = 36 J; KE_f = ½×6×4 = 12 J; loss = 24 J (two-thirds!). Shortcut: ΔKE = ½μu² = ½×(8/6)×36 = 24 J.
Q5 — Inelastic & Perfectly Inelastic Collisions · hard · numerical
A 10 g bullet at 400 m/s embeds into a 1.99 kg block hanging as a ballistic pendulum. The height to which the block+bullet swings is:
A. 0.1 m
B. 2 m
C. 0.4 m
D. 0.2 m ✓ Correct
Solution: v_common = 0.01×400/2 = 2 m/s; h = v²/2g = 4/20 = 0.2 m. Trap: never equate bullet KE to mgh — most KE is lost in embedding.
Q6 — Inelastic & Perfectly Inelastic Collisions · medium · numerical
Two identical cars moving at equal speeds v collide head-on and lock together. The wreckage moves at:
A. 2v
B. v
C. Zero ✓ Correct
D. v/2
Solution: Equal and opposite momenta cancel: the combined wreck stops; ALL the kinetic energy is dissipated.
Q7 — Inelastic & Perfectly Inelastic Collisions · hard · numerical
A 1 kg ball moving east at 4 m/s collides with and STICKS to a 1 kg ball moving north at 3 m/s. The speed of the combined mass is:
A. 1 m/s
B. 5 m/s
C. 2.5 m/s ✓ Correct
D. 3.5 m/s
Solution: p⃗ = (4, 3) kg·m/s, |p| = 5; v = 5/2 = 2.5 m/s at tan⁻¹(3/4) north of east — vector addition, not scalar.
Q8 — Inelastic & Perfectly Inelastic Collisions · medium · numerical
A 2 kg block at 10 m/s hits an 8 kg block at rest and sticks. The percentage of kinetic energy lost is:
A. 80% ✓ Correct
B. 50%
C. 64%
D. 20%
Solution: Retained = m₁/(m₁+m₂) = 2/10 = 20% ⇒ 80% lost. Shortcut: fraction lost = m₂/(m₁+m₂).