# Easy momentum question

## Homework Statement

A 30.00 kg mass falls from a height of 4.00m. The momentum of the mass just before it hits the ground is?

obviously p=mv

## The Attempt at a Solution

I just can't figure out how to get a velocity for this formula?

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LowlyPion
Homework Helper

## Homework Statement

A 30.00 kg mass falls from a height of 4.00m. The momentum of the mass just before it hits the ground is?

obviously p=mv

## The Attempt at a Solution

I just can't figure out how to get a velocity for this formula?
Consider one of these kinematic equations:
https://www.physicsforums.com/showpost.php?p=905663&postcount=2

Matterwave
Gold Member
There are 2 ways to do this.

1) Find the velocity using kinematic equations:
$$x = \frac{1}{2}gt^2$$
you know x and g so you can solve for t. After solving for t you can get the velocity from $$v=gt$$.

2) You can also use energy conservation
$$KE=\frac{1}{2}mv^2=PE=mgh$$
and then applying the knowledge of what KE is and momentum is
$$KE=\frac{p^2}{2m}$$
to find p directly.

yes sir that helped me figure out what the book got, thanks a bunch!