SAT Subject Physics Practice Question 247: Answer and Explanation

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Question: 247


A simple pendulum, composed of a bob of mass m connected to the end of a massless rod, executes simple harmonic motion as it swings through small angles of oscillation. The largest angle the pendulum makes with the vertical is denoted by θmax. Frictional effects are negligible and can be ignored, and the pendulum is near the surface of the earth, where g = 9.8 m/s2.

Which one of the following statements is true?

A. At θ = 0, the tangential acceleration is 0.
B. At θ = θmax, the tangential acceleration is 0.
C. At θ = 0, the speed is 0.
D. At θ = 0, the restoring force is maximized.
E. At θ = θmax, the speed is maximized.

Correct Answer: A


At the instant a simple harmonic oscillator passes through equilibrium, the restoring force is zero. Since the restoring force on the bob is zero at equilibrium, the tangential acceleration of the bob is also zero at this point.

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