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tsw99
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Homework Statement
I encountered this past exam paper question in Hong Kong when I was giving tutorial to a high school student. I am confused with the answer provided by the official authority. The question is (in exact wordings):
An electrical toy car of mass m goes up an inclined plane of inclination 30° with constant speed v. The friction acting on the car is half of the weight of the car. What is the average power of the car?
A. 1/2 mgv B. mgv C. 3/2 mgv D. 2mgv
Homework Equations
The Attempt at a Solution
The friction f provides by the ground to propel the car is exactly canceled by the component of weight down the inclined plane, hence the power is fv which is equal to mg(sin30°)v=1/2 mgv which is A. However the official answer is B. I have no idea how to arrive at the answer B and I believe the authority must have their own grounds. I even think that B is a "trap" choice when I first read this question.
Any help is appreciated. Thanks.