Question

A 7.80-g bullet moving at 530 m/s penetrates a tree trunk to a depth of 6.2 cm.
(a) Use work and energy considerations to find the average frictional force that stops the bullet.

(b) Assuming the friction force is constant, determine how much time elapses between the moment the bullet enters the tree and the moment it stops moving

Answer 1

change in KE =1/2mv^2
1/2(.0078)(530)^2=1095.51 kg*m^2/s^2
6.2 cm = .0062 m
1095.51/.0062 = 176,695 N= F

Answer 2

What formula did you use?
Why did you divide the KE with the depth of the penetration?