Physics Momentum

Question

A man with a mass of 54 kg and a boy with a mass of 27 kg push against each other while they are standing on ice skates on a frozen pond. If the man moved away from the boy with a velocity of 4.5 m/sec, what is the velocity of the boy?

Answer 1

We know that the mass of a boy m = 27 kg, mass of a man M = 54 kg; the man moved away with the velocity V = 4.5 m / s.

To find the velocity of the boy, we will use the law of conservation of linear momentum. Before the interaction they are not moving, hence the total linear momentum is 0. After interaction they are moving in opposite direction.

Let's choose the coordinate axis x to the right in the direction of the velocity of the man after interaction, then we have

0 = MV - mv,

from this equation we will get for the velocity of the boy

v =(M/m) V

After substituting the numerical values, we obtain that

v = (54 kg /27 kg) 4.5 m/s = 9 m/s

Answer: 9 m/s