# Average Force

## Homework Statement

a proton (m= 1.67 x 20E027kg) that has a speed of 5.0 x 10E6m/s passes thru a metal film of thickness 0.010mm and emerges with a speed of 2.0 x 10E6m/s. how large an average force opposed its motion thru the film?

KE=.5mvE2
P=mv (momentum)

## The Attempt at a Solution

I tried to plug the above equations and nothing works. to be honest I am completely lost. What am I to do? the answer suggests that the force is going N - why if its opposing and its going thru the film it should be going in the opposite direction? Do I use gravity - I have no idea what is expected of me or what they are asking in the first place.

rock.freak667
Homework Helper
You can ignore gravitational effects since the mass is quite small.

However, you can apply conservation of energy and easily solve this problem.

An alternative to the above:

You know the initial speed, the final speed and the distance travelled.

Plug that into one of the equations of motion and you'll get the acceleration.

From that you can use F=ma to get the force.

SammyS
Staff Emeritus