Homework Help: Bullet and block collision

1. Oct 15, 2006

mikefitz

A 0.01-kg bullet traveling horizontally at 400.1 m/s strikes a 4.2-kg block of wood sitting at the edge of a table. The bullet is lodged into the wood. If the table height is 1.3 m, how far from the table does the block hit the floor?

I have calculated the final velocity of the bullet and block to be:

.01(400.1)=.01(Vf)+4.2(Vf)

Vf= .9504 m/s

So, now I have the velocity of the bullet embedded into the block. The time in the air is 1.3/9.82 = .1325 seconds.

.1325s * .9504 m/s = .1259 meters

Why is this wrong? Thanks

2. Oct 15, 2006

Staff: Mentor

How did you determine this? How long does it take for something to fall 1.3 meters?

3. Oct 15, 2006

OlderDan

Your calculated time in air is wrong.

4. Oct 15, 2006

mikefitz

Sorry, I meant to type 1.3/9.81 = .1325 -- the 9.82 was a typo.

5. Oct 15, 2006

OlderDan

That is not the problem. You are not calculating time. It would help you to keep your units in your calculations. Distance divided by acceleration is not time.

6. Oct 15, 2006

mikefitz

Stupid me, I used this formula and found the correct answer: http://www.glenbrook.k12.il.us/gbssci/Phys/Class/1DKin/U1L6b4.gif [Broken]

thanks!

Last edited by a moderator: May 2, 2017