physics
posted by Janus .
For a ballistics study a 1.9 gram bullet is fired into soft wood at 380 meters/sec and penetrates 15 cm.
a.) find the retarding force (resistance) in N.
b.) the time needed to stop the bullet in sec.
c. acceleration of the bullet in meters/sec.

a) initial kinetic energy = (force) x (penetration distance)
Solve for the force, F = .
Use kg and meters for doing the calculation.
b) Vaverage * time = (Vo/2)*time = 0.15 m
Solve for the stopping time.
Vo is the initial velocity, 380 m/s
c) a = F/m = Vo/(stopping time)
(You should get the same answer wither way) 
f=2.41N