Question

If a boy (m = 25 kg) at rest on skates is pushed by another boy who exerts a force of 500 N on him and if the first boy's final velocity is 20 m/s, what was the contact time?

Answer 1

1 second

Step-by-step explanation:

The impulse exerted on the boy is equal to its change of momentum:

`I = \Delta p\\F \Delta t = m \Delta v`

where

F = 500 N is the push on the boy

`\Delta t` is the contact time

m = 25 kg is the mass of the boy

`\Delta v = 20 m/s` is the change in velocity of the boy

Solving the formula for the contact time, we find

`\Delta t=(m\Delta v)/(F)=((25 kg)(20 m/s))/(500 N)=1 s`