# Average friction force(energy)

## Homework Statement

A 16 g bullet pierces a sand bag 13cm thick. If the initial bullet velocity was 51m/s and it emerged from the sandbag with 14m/s, what is the average magnitude of the friction force the bullet experienced while it traveled through the bag?

k+u=k+u?

## The Attempt at a Solution

I am completely stumped on this equation, i think my problem is that i keep thinking kinematics but i dont believe that is how we are supposed to solve it as we are currently working on energy