# Bullet hitting wood

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

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#### russ_watters

Mentor
Why don't you show us what you've tried so far.

watters

I need help starting it! I'm sort of confused. Thanks for your time.

#### ShawnD

A 5.5 g bullet is fired into a block of wood with a mass of 22.6g. The wood block is intially at rest on a 1.5m tall post. After the collision, the wood block and bullet land 2.5m from the base of the post. Find the initial speed of the bullet.
Ah the great many many many step question.

First find the time it took to fall the 1.5m using this equation

$$d = V_it + \frac{1}{2}at^2$$

Since you know the time and the horizontal distance, find the horizontal velocity using this formula

$$V = \frac{d}{t}$$

Now that you know the horizontal velocity of the block and and the bullet, you can also find and compare the inertia. Subscript bu will be bullet and bl will be block.

$$(V_b_u) (m_b_u) = (V_b_u_+_b_l) (m_b_u_+_b_l)$$

I hope I didn't leave anything out.

#### Integral

Staff Emeritus
Gold Member
Here is a recent thread dealing with this problem.

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