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 [ Return to question menu ] Answer 1 9.8m/s2 INCORRECT 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. Try return to top Answer 2 15m/s2 INCORRECT 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. Try  return to top Answer 3 3.0 m/s2 CORRECT 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. return to top Answer 4 53 m/s2 INCORRECT This is the average of the 2 given velocities of the car and does not deal with acceleration. Try  return to top 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? return to top 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.