MCAT Physics Question 9: Answer and Explanation

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Test Information

Question: 9

9. A 20 kg wagon is released from rest from the top of a 15 m long lane, which is angled at 30° with the horizontal. Assuming that there is friction between the ramp and the wagon, how is this frictional force affected if the angle of the incline is increased?

  • A. The frictional force increases.
  • B. The frictional force decreases.
  • C. The frictional force remains the same.
  • D. It cannot be determined from the information given.

Correct Answer: B

Explanation:

The force of friction on an object sliding down an incline equals the coefficient of friction times the normal force. The normal force is equal in magnitude to the perpendicular component of gravity, which is given by mg cos θ. As θ increases, cos θ decreases. Therefore, the normal force and frictional force decrease as the angle of the incline increases.

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