Question

You see a pair of shoes tied together by the laces and hanging over a telephone line. You throw a 0.21-kg stone at one of the shoes (mass = 0.35 kg), and it collides elastically with the shoe with a velocity of 1.8 m/s in the horizontal direction. How far up does the shoe move?

Answer 1

Assume the rock hits a single shoe side-on and that kinetic energy and momentum are conserved on impact. The mass of a single shoe is 0.175 kg. Since that is approximately equal to the stone's mass, the shoe will acquire a velocity approximately equal to the stone's velocity before collision.

(You should work that out on your own).

From the velocity of the single shoe after impact (about 1.8 m/s), calculate how far it will rise while hanging by a shoestring.