SAT Subject Physics Practice Question 248: Answer and Explanation

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Question: 248


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.

Knowing which one of the following would enable you to calculate the length of the pendulum?

A. The mass of the bob
B. The period of the oscillations
C. The tangential acceleration at θ = 0
D. The maximum speed of the bob
E. The acceleration at θ = θmax

Correct Answer: B


Using the equation for the period of a simple pendulum (oscillating with a small amplitude so we can approximate the motion as simple harmonic), T = , we see that we can solve for L if we know T (since g is known).

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