# Kinetic Motion

1. Jul 6, 2006

### Hollysmoke

A 8.0g bullet travelling at 400m/s passes through a heavy block of wood in 4.0x10^-4s, emerging with a velocity of 100m/s. Ignore the motion of the wood.

1) What is the force exerted by the block on the bullet?
2) What is the force exerted by tbe bullet on the block?
3) How thick is the bullet?

I've gotten 1 and 2 but I have no idea how to solve the 3rd one. Can someone please help me out?

2. Jul 6, 2006

### Hollysmoke

a= -750,000m/s^2
F = 6000N

Just to save time

3. Jul 6, 2006

### Staff: Mentor

I'm going to take a wild guess and say that the last question is a typo and that it should have read: How thick is the wood?

4. Jul 6, 2006

### Hollysmoke

I really hope so, because the sheet says "bullet".

5. Jul 6, 2006

### Hollysmoke

If Icalculate the wood, do I do the following:

100^2 -400^2 = 2(-750,000)d

d=0.1m

6. Jul 6, 2006

### Staff: Mentor

Looks good to me.

7. Jul 6, 2006

### Hollysmoke

Also, for this question:

The Easter Bunny runs along a straight and narrow path with a constant speed of 25m/s. He passes a sleeping tortoise, which immediately starts to chase the bunny with a constant acceleration of 3x10^-3m/s^2. How long does it take to catch up to the bunny?

I did this:

v=dt
d=vt
d=25m/st

25t= 1/2(3.0x10^-3m/s^2)t^2
t = 16,667 seconds, or 4.63 hours.

8. Jul 6, 2006

### Staff: Mentor

Looks good. (Just be careful when you are writing up your steps--assuming you need to show your work. Don't write something like "v=dt" when you mean "v=d/t".)

9. Jul 6, 2006

### Hollysmoke

Okay. Thanks for confirming my answers