A 4.17 g bullet moving at 506.1 m/s penetrates

a tree trunk to a depth of 4.64 cm.
a) Use work and energy considerations to
find the magnitude of the force that stops the
bullet.
Answer in units of N.

b) Assuming that the frictional force is constant,
determine how much time elapses between
the moment the bullet enters the tree
and the moment the bullets stops moving.
Answer in units of s.

1 answer

m = .00417 kg
distance = .0464 meter

F * distance = work

F = (1/2) m v^2 / .0464

b) easy way is if acceleration is constant then average speed = (initial + final)/2
so
average speed = 506.1/2
distance = .0464
so
time = .0464/253 = 1.83*10^-4 seconds
= 0.000183 seconds