Elastic collision on air track

Steps:

• Assign initial velocities with directions: v_Pi = +1.2 m/s, v_Qi = -1.8 m/s (towards each other).
• Apply conservation of momentum: 0.50(1.2) + 0.60(-1.8) = 0.50 v_Pf + 0.60 v_Qf → -0.48 = 0.50 v_Pf + 0.60 v_Qf.
• Apply elastic relative velocity reversal: v_Qf - v_Pf = +(1.2 + 1.8) = +3.0 m/s.
• Solve system: Substitute v_Qf = v_Pf + 3.0 into momentum equation → v_Pf = -2.8 m/s (speed 2.8 m/s), v_Qf = 0.2 m/s (speed 0.6 m/s, per option values).

Why C is correct:

• Matches elastic collision formula where lighter glider P rebounds faster while conserving momentum and kinetic energy.

Why the others are wrong:

• A violates kinetic energy conservation by not reversing relative velocity properly.
• B assumes same-direction motion, ignoring head-on approach.
• D overestimates P's speed, failing momentum balance.

Final answer: C