Physics Review QuestionUnit:
MechanicsYear:
1991 Question#:
6Question:
A child riding a bicycle at 15 meters per second decelerates at the rate of 3.0 meters
per second^{2} for 4.0 seconds. What is the child's speed at the end of the 4.0 seconds?(1
) 12 m/s(2
) 27 m/s(3
) 3.0 m/s(4
) 7.0 m/sWhat is this question really asking?
Explanation by: Alon B [ Return to question menu
]Answer 1
12 m/s INCORRECT This answer is incorrect. It looks like you found the change in velocity but a change is not the same thing as the final velocity. If you are using the acceleration formula make sure your number for acceleration has a minus in front of it because the child is decelerating. This is the formula you want to be using. return to top
Answer 2
27 m/s INCORRECT This answer is incorrect because if you used the right equation (acceleration) and plugged in the right numbers you shouldn't be getting 27 m/s. It looks like you added your change in velocity to the original velocity instead of subtracting them. When you are using the acceleration formula make sure your number for acceleration has a minus in front of it because the child is decelerating. return to top
Answer 3
3.0 m/s CORRECT This answer is the correct one. The formula acceleration = final velocity - initial velocity / change in time will give the correct answer 3.0 m/s. ( -3 = Vf - 15m/s divided by 4s) return to top
Answer 4
7.0 m/s INCORRECT This answer is incorrect because if you used the right equation (acceleration) and plugged in the right numbers you shouldn't be getting 7.0 m/s. Looks like you may have added the accceleration to the time. return to top
What's this question really asking?
This question is asking wether or not you know a way to find the final velocity while knowing the acceleration, and change in time and the initial velocity. It is important to remember that when decelerating the number will always be a negative number. return to top |

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