Physics Review Question

Unit: Mechanics
Year: 1992 Question#: 1
Question: The velocity of a car changes from 60. meters per second north to 45 meters per second north in 5.0 seconds. The magnitude of the car's acceleration is
(1 ) 9.8m/s2
(2 ) 15m/s2
(3 ) 3.0m/s2
(4 ) 53m/s2
What is this question really asking?

Explanation by: Jennifer I

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Answer 1

9.8m/s2 is the acceleration caused by gravity without a direction. If the car was accelerating at this rate it would be free falling.
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Answer 2

This is the difference in the velocities of the car (60m/s-45m/s = 15m/s). This answer would be correct if the question had asked for the change in velocity of the car but the answer does not deal with acceleration.
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Answer 3
3.0 m/s2

a= (45m/s-60m/s) / 5.0sec
a= -3m/s2
The negative sign shows that the car is slowing down (deccelerating). This is not relevent in this question since the question only asked for the magnitude of the car's acceleration.
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Answer 4
53 m/s2

This is the average of the 2 given velocities of the car and does not deal with acceleration.
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What's this question really asking?

What is the acceleration of a car which changes velocity from 60 m/s north to 45 m/s north in 5 seconds?
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