SAT Subject Physics Practice Question 549: Answer and Explanation

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Question: 549

5. A person standing in an elevator watches a spider hanging from a thread attached to the ceiling. Suddenly the elevator accelerates downward. The person watching the spider on the thread will see

A. the spider thread snap and the spider slowly fall.
B. the spider thread and spider float upward.
C. the spider thread snap and the spider slowly float upward.
D. the spider thread and the spider remain as they were before the acceleration began.
E. the spider thread begin to swing back and forth like a pendulum.

Correct Answer: D

Explanation:

The correct answer is (D). The acceleration affects the spider in the same way that it affects the observer. If the elevator were in free fall, everything in the elevator would free fall together, including the spider. If the elevator accelerates upward, the spider experiences an apparent gain in weight, just as a person riding in the elevator does.

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