# Back again, Another question about friction

1. Feb 13, 2006

### Moomba44

Hey again, once again I have no idea where to start on an equation that I recieved on a quiz

A 70 kg skater initially moving at 10.0 m/s across the ice drags the rough part of one skate along the ice, slowing herself to 4.0 m/s over a 2.0 s period of time. What is the magnitude (a positive number) of the frictional force on her during the time she is slowing down? [Assume her acceleration is constant.]

I did some models with force diagrams and such on my own, but once again I couldn't really figure out anything from them. If someone could once again point me in the right direction generally on how to go about this I would be extremely greatful. Thank you in advance.

2. Feb 13, 2006

### arildno

1.How can the acceleration be written in terms of the frictional force and the skaters mass?
2. since the acceleration is constant, how does the velocity of the skater vary with time?

3. Feb 14, 2006

### andrevdh

Try to calculate the acceleration of the skater from the given initial and final velocities for the 2.0 s interval using your constant acceleration equations. One you've got that the frictional force can be calculated from Newton's second law, since it is this force that caused that particular acceleration.