Elastic collision between ball and train · CAP 2005 #1

Physics · mechanics

Problem

A child throws a ball toward the front end of an approaching train. The collision between the ball and the train is perfectly elastic. Let

v

be the speed of the ball with respect to the train and

V

its speed with respect to the ground. If the labels "i" and "f" refer to those speeds just before and just after, respectively, the ball hits the train, then (a)

v_i = v_f

and

V_i < V_f

; (b)

v_i < v_f

and

V_i < V_f

; (c)

v_i > v_f

and

V_i < V_f

; (d)

v_i = v_f

and

V_i > V_f

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