Physics Review QuestionUnit:
mechanicsYear:
1988 Question#:
8Question:
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 secondWhat 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 |

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