The percentage and force of Friction ( 9/28/09)

[sumo87]

Homework Statement

Hi everyone,

I have 2 quick Questions, about my HW so if u think u can give me a hit please post.

Homework Equations

the Question was :-

10g bullet is fired into a ballistic pendulum made from a 4kg wood block and two light cords. The block's vertical displeacment is 5 cm.

1-

what is the inital velocity.

what percentage of the bullet's initial kinetic energy is lost in the collision

what is the force of friction acting on the bullet in the block assuming that it stops in 3 cm

The Attempt at a Solution

I found the initial velocity into the equation

1/2mv^2 = mgh

and i got 19.8 m/s

so please help me with 2nd and the 3rd Qs

 

[sumo87]

k i got for the 3ed Q

1.5E-3

I used the equation

F= ma