physics
posted by monic .
A 7.80g bullet moving at 520 m/s penetrates a tree trunk to a depth of 4.60 cm.
(a) Use work and energy considerations to find the average frictional force that stops the bullet.
N
(b) Assuming the frictional force is constant, determine how much time elapses between the moment the bullet enters the tree and the moment it stops moving.
s

(a) (Avg. Force) x (penetration distance) = Initial kinetic energy
Fav = (M/2)Vo^2/(0.046 m)
= ___ Newtons
(b) (Penetration distance)/(average speed) = 4.60*10^2 m/260 m/s
= 1.77*10^4 s 
69^2=5