A 2-kg object moves at 3 m/s and collides with a stationary 4-kg object. If the collision is perfectly elastic, what is the final velocity of the 2-kg object?
A−1 m/s
B+1 m/s
C−3 m/s
D+3 m/s
Explanation
📌 For 1D elastic collision, use both conservation of momentum and KE. Result: v₁f = ((m₁ − m₂)/(m₁ + m₂))·v₁i = ((2 − 4)/(2 + 4))(3) = −1 m/s (bounces back). Distractor B: forgot the negative from mass ratio; C: used initial speed with wrong sign; D: assumed no change.