# Ballistics pendulum - sort of - COM

1. Jun 9, 2010

### pat666

1. The problem statement, all variables and given/known data
A 4.00-g bullet, travelling horizontally with a velocity of magnitude 400 m/s, is fired into
a wooden block with mass 0.800 kg, initially at rest on a level surface. The bullet passes
through the block and emerges with its speed reduced to 120 m/s. The block slides a
distance of 45.0 cm along the surface from its initial position.
(i) What is the coefficient of kinetic friction between block and surface?
(ii) What is the decrease in kinetic energy of the bullet?
(iii)What is the kinetic energy of the block at the instant after the bullet passes through it?

We have a physics exam coming up and they gave us a couple of practice questions with no answers. I solved these but im unsure if there correct can someone please take a look. thanks

i) 0.221996
ii) 291.2J
iii) 0.784J - i actually found this one while solving i) i used W=Fs i think you can use kinematics for acceleration and the use F=ma

2. Relevant equations

3. The attempt at a solution

2. Jun 10, 2010

### collinsmark

'Got a little crazy with the precision in i), huh? :tongue: But seriously though, the answers look ok to me.

3. Jun 10, 2010

### pat666

yeah i guess i did. thanks