Momentum question?

Question

A horizontal moving walkway is moving at 9 m/s. On average, 9 people per second step on to it, and 9 people per seond step off of it. Assuming that the people are approximately motionless with respect to the walkway, and that the average mass of a person is 60 kg, what average driving force is required to keep the walkway moving at a constant speed?

ok, i dont really understand the problem, can someone explain it?

Answer 1

9 m/s! I wouldn't want to get on or off that walkway.

Every second 9 people are accelerated from 0 m/s to 9 m/s. Their energy and momentum are lost to the system when they get off.

change in momentum = 9*(60kg)*(9m/s) = Force*(1 second)

Force = 9*9*60 = 4860 N.