# Find the initial speed of the bullet!

1. Feb 2, 2004

### vangjo

A 5.5 gram bullet is fired into a block of wood with a mass of 22.6 grams. The wood block is initially at rest on a 1.5 meter tall post. After the collision, the wood block and the bullet land 2.5 meters from the base of the post. Find the initial speed of the bullet.

2. Feb 3, 2004

### Integral

Staff Emeritus
This is a 2 part problem. First you need to find the initial velocity of the block using the equations of motion for a falling body.

Find the time the block was falling with

$$\frac {-gt^2} 2 + V_y(0)+y(0)$$

Then assume that the block had its full x velocity before it started to drop so

$$X(t)= V_x t$$

Also use conservation of momentum

$$M_{bullet}V_{bullet}= M_{Block + Bullet} V_{Block}$$

That should get you started.