SAT Subject Physics Practice Question 68: Answer and Explanation

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Question: 68

5. A sphere of charge +Q is fixed in position. A smaller sphere of charge +q is placed near the larger sphere and released from rest. The small sphere will move away from the large sphere with

A. decreasing velocity and decreasing acceleration.
B. decreasing velocity and increasing acceleration.
C. decreasing velocity and constant acceleration.
D. increasing velocity and decreasing acceleration.
E. increasing velocity and increasing acceleration.

Correct Answer: D


The acceleration of the small sphere is

As r increases (that is, as the small sphere is pushed away), a decreases. However, since a is always positive, the small sphere’s speed, v, is always increasing.

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