What is the Average Friction Force Experienced by a Bullet Piercing a Sandbag?

[juggalomike]

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?

Homework Equations

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 don't believe that is how we are supposed to solve it as we are currently working on energy

 

[rl.bhat]

Work done due to frictional force = change in KE.

 

[juggalomike]

lol thanks