# Linear Momentum and Collisions of meteor

A meteor whose mass was about 10^8 kg struck the Earth (m = 6.0 X10^24 kg) with a speed of about 11 km/s and came to rest in the Earth.
(a) What was the Earth's recoil speed? (m/s)

(b) What fraction of the meteor's kinetic energy was transformed to kinetic energy of the Earth? (%)

(c) By how much did the Earth's kinetic energy change as a result of this collision? (J)

I know this problem requires a look at conservation of momentum and conservation of energy principles, but I am having trouble just trying to start this problem out :grumpy:

## Answers and Replies

dextercioby
Science Advisor
Homework Helper
You know that u need to apply the law of conservation of momentum.Well,then do it...I'm afraid you're dealing with a plastic collision for which the KE is not really conserved...

Daniel.

HallsofIvy
Science Advisor
Homework Helper
This is a "completely inelastic" collision- Kinetic energy is not conserved so you cannot use that.

You do, however, know that the earth has 0 velocity initially and that both the earth and the asteroid have the same velocity after.

Mava+ Meve= Mav'a+ Mev'e ("e" subscripts are "earth", "a" subscripts are "asteroid". v' is after the collision.) becomes Mav= (Ma+ Me)v'.

You know Ma, Me, and v. Solve for v'. Once you know that you can calculate the kinetic energy of the asteroid and earth after the collision and compare it with those values before the collision.