# Homework Help: Momentum and impulse?

1. Jan 10, 2010

### Air_force_two

I'm a little confused about momentum and impulse.
Its not a single problem but just how they relate.

For example if a 2kg block moving at 3 m/s hits a 6 kg block,
then it will move 1 m/s because momentum is conserved with
6 momentos on either side of the equation. If the impact time is 1 millisecond
whats the impulse? I dont know how you get impulse from momentos.
Impulse is force x delta time and Momentum is mass x velocity, but in this problem
how do i get impulse using the fact that the system's momentum is 6 momentos.

2. Jan 10, 2010

### carnifex

Airforcetwo,
What you have to understand is that Change in Momentum = Impulse, as described in the equation F delta T=m delta v. So in this case, it is not 6 momentos on either side, but 6 momentos combined because the initial Momentum must equal the final Momentum, which is the Momentum of both blocks added together.
-C

Last edited: Jan 10, 2010
3. Jan 10, 2010

### Matterwave

We have Newton's second law:

$$F=ma$$

This can be expressed as:
$$F=m\frac{dv}{dt}=\frac{d(mv)}{dt}=\frac{dp}{dt}$$

Assuming the mass doesn't change. Now, if we integrate both sides with respect to time, we get the impulse I: (assume correct limits of integration)

$$I=\int{Fdt}=\int{\frac{dp}{dt}dt}=\int{dp}=\Delta p = p_f-p_i$$
Therefore, the impulse is simply the change in momentum.