Physics Review Question

Unit: mechanics
Year: 1988 Question#: 8
Question: A 20-Kilogram car traveling east at 6 meters per second collides with a 30-Kilogram car that is traveling west. If both the cars come to rest immediately after the collision, what was the speed of the west bound car just before the collision?

(1 ) 6 meters per scond
(2 ) 2 meters per second
(3 ) 3 meters per second
(4 ) 4 meters per second

What is this question really asking?




Explanation by: Cory V

[ Return to question menu ]













Answer 1
6 m/s

INCORRECT

If the west bound car was travelling at 6 meters per second the they would not have come to a complete stop after the collision. The west bound car would have over powered the east bound car because of the mass difference. return to top























Answer 2
2 meters per second

INCORRECT

If the west bound car was travelling at 2 meters per second it would not have enough momentum to cancel out the momentum of the east bound car which would have brought them both to a stop after the collision. return to top



























Answer 3
3 meters per second

INCORRECT

If the west bound car was travelling at 3 meters per second it still would not have enough momentum to cancel out that of the east bound car. return to top


























Answer 4
4 meters per second

CORRECT

You remembered that in a collision, momentum is conserved. The total momentum before the collision must be equal to the total momentum after the collision. The question tells you the cars stop so you know the total momentum after the collision must be zero kgm/s.
p=mv will give you the momentum of the east bound car, if you divide the momentum by the mass of the west bound car, the result will be the velocity that you are solving for. If you plug 4 m/s into P=MV you will end up with a momentum of 120kgm/s which cancels out the momentum of the other car, this will be a check for your answere. return to top


























What's this question really asking?

A 20-kilogram car travelling east with a speed of 6 meters per second collides with a 30-kilogram cart travelling west. If both cars come to rest immediatly after the collision, what was the speed of the west bound car just before the collision? return to top

[Home]  [Lessons]  [Review]    [Links]

This web site is designed and maintained by Science Joy Wagon and may not be reproduced or redistributed without written permission from Science Joy Wagon.
Contact with comments.