# What Equation?

1. Mar 24, 2004

### Draygon_Phly

Hi! I would like to know what equation I would use to figure out this question and why?

A 10-gram bullet is fired into a 3.0-kilograme block, given that the block a velocity of 30 cm/sec. With what velocity was the bullet fired?

2. Mar 24, 2004

### Chen

The conservation of momentum:
$$m_1v_1 + m_2v_2 = m_1u_1 + m_1u_2$$
So that:
$$m_$$ - mass of each object
$$v_$$ - velocity of each object before impact
$$u_$$ - velocity of each object after impact

Do you need more help or can you figure this out yourself now?

3. Mar 24, 2004

### Draygon_Phly

thanx I can figure it out from here.