# Thread: Momentum

1. ## Momentum

An animal-rescue plane flying due east at 23 m/s drops a bale of hay from an altitude of 60 m.

The acceleration due to gravity is
9.81 m/s^2

If the bale of hay weighs 177 N; what is the
momentum of the bale the moment it strikes
the ground? Answer in units of kgm/s.

OK, I don't know what to do with this one. I use a kinematics equation to find the velocity when the bale hits the ground (I get Vf = 34.31m/s) and then I divide the 177N by 9.81 to get it's weight in kg. I multiply that mass by the Vf to get 619, but apparently that answer is wrong. Any insight?

2. Remember, momentum is a vector. It has both a horizontal and vertical component (assuming no air resistance). Find the resultant velocity by pythagoras seeing you know both componential velocities (and find the direction if you need it). Then, calculate the momentum $\vec{p} = m\vec{v}$ where m can be found, as you've said, by its weight.

3. RIGHT! I should've known there was something wrong with that, thanks for adding in the missing piece

4. Or you could find the final velocity directly by using conservation of energy.

-Dan