Elastic Collisions (1D & 2D) — JEE Main Physics MCQs with Solutions
Free JEE Main Physics Elastic Collisions (1D & 2D) 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 — Elastic Collisions (1D & 2D) · easy · theory
In a perfectly elastic collision, the quantities conserved are:
A. Both linear momentum and kinetic energy ✓ Correct
B. Neither
C. Only momentum
D. Only kinetic energy
Solution: Elastic: p⃗ and KE both conserved. (Momentum is conserved in ALL collisions; KE only in elastic ones.)
Q2 — Elastic Collisions (1D & 2D) · medium · theory
In a 1D elastic collision between two EQUAL masses (one initially at rest), after the collision:
A. They exchange velocities — the mover stops, the target moves off with the original velocity ✓ Correct
B. The mover rebounds
C. They stick together
D. Both move at half speed
Solution: Equal-mass elastic exchange: v₁' = 0, v₂' = u. Seen in billiards and in neutron moderation by hydrogen.
Q3 — Elastic Collisions (1D & 2D) · easy · numerical
A 2 kg ball at 6 m/s hits an identical stationary ball head-on, perfectly elastically. The speeds after are:
A. 3 and 3 m/s
B. 0 and 6 m/s ✓ Correct
C. 2 and 4 m/s
D. 6 and 6 m/s
Solution: Equal masses exchange velocities: the incoming ball stops; the struck one leaves at 6 m/s.
Q4 — Elastic Collisions (1D & 2D) · medium · numerical
A ball of mass m at speed u strikes a much HEAVIER wall elastically and head-on. It rebounds with speed:
A. u (same speed, reversed) ✓ Correct
B. 2u
C. Zero
D. u/2
Solution: Limit m₂ → ∞: v₁' = −u. The wall barely moves but reverses the ball's momentum.
Q5 — Elastic Collisions (1D & 2D) · hard · numerical
A 2 kg ball at 9 m/s strikes a 1 kg stationary ball elastically head-on. Their final velocities are:
A. 3 m/s and 12 m/s ✓ Correct
B. 4.5 m/s each
C. 6 m/s and 3 m/s
D. 0 and 9 m/s
Solution: v₁' = (m₁−m₂)u/(m₁+m₂) = (1/3)×9 = 3 m/s; v₂' = 2m₁u/(m₁+m₂) = (4/3)×9 = 12 m/s.
Q6 — Elastic Collisions (1D & 2D) · medium · numerical
In an elastic head-on collision, a neutron (mass 1) strikes a carbon nucleus (mass 12) at rest. The fraction of its kinetic energy transferred is:
A. 4/13
B. 100%
C. 48/169 ≈ 28% ✓ Correct
D. 1/12
Solution: Fraction = 4m₁m₂/(m₁+m₂)² = 48/169 ≈ 0.28 — why light moderators (hydrogen) beat carbon.
Q7 — Elastic Collisions (1D & 2D) · hard · numerical
A ball strikes an identical ball at rest elastically; the incident ball is deflected 30° from its original line. The struck ball moves at an angle from that line of:
A. 90°
B. 60° (on the other side) ✓ Correct
C. 45°
D. 30°
Solution: Equal-mass elastic ⇒ 90° between finals: 90° − 30° = 60° on the opposite side.
Q8 — Elastic Collisions (1D & 2D) · medium · numerical
In a 1D elastic collision of a 1 kg ball at 8 m/s with a 3 kg ball at rest, the incident ball's final velocity is:
A. +2 m/s
B. −4 m/s (rebounds) ✓ Correct
C. −8 m/s
D. +4 m/s
Solution: v₁' = (1−3)/(1+3) × 8 = −4 m/s — lighter projectile bounces back off a heavier target.