AP Physics 1 Question 160: Answer and Explanation

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Question: 160


In the laboratory, a cart of mass m is held in place on a smooth incline by a rope attached to a spring scale, as shown in the figure. The angle of the incline from the horizontal θ varies between 0° and 90°. A graph of the reading in the spring scale as a function of the angle θ is produced. Which of the following will this graph look like?

  • A.
  • B.
  • C.
  • D.

Correct Answer: C


C-The cart is in equilibrium, so the spring scale's force is equal to the component of the cart's weight that acts parallel to the plane. That component is mg sinθ. Thus, the graph of spring scale reading vs. θ should be a sine function, as in choice C. Choice B is wrong because that's what a sine function looks like all the way to 180°; here, the angle of the incline only goes to 90°.