physics question

Question

A 7.80-g bullet moving at 460 m/s penetrates a tree trunk to a depth of 6.40 cm.?

(a) Use work and energy considerations to find the average frictional force that stops the bullet.


(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.

Answer 1

Hi 

 In this problem the kinetic energy lost by the bullet is equal to the work done 

KE =Average  Force  * displacement 

1/2 M V² = Force * 6.4 * 10 ^-2

or 1/2( 7.8* 10 ^-3 * 460 * 460) =  Force * 6.4* 10^-2

Find Force 

For time 

t= (initial speed * mass)/ Force  Her we have changed mass in kg and distance in m and so the force will be in N