SAT Subject Physics Practice Question 21: Answer and Explanation

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Question: 21

12. At the surface of the earth, an object of mass m has weight w. If this object is transported to an altitude that’s twice the radius of the earth, then, at the new location,

A. its mass is and its weight is
B. its mass is m and its weight is
C. its mass is and its weight is
D. its mass is m and its weight is
E. its mass is m and its weight is

Correct Answer: E

Explanation:

Mass is an intrinsic property of an object and does not change with location. This eliminates A and C. If an object’s height above the surface of the earth is equal to 2RE, then its distance from the center of the earth is 3RE. Thus, the object’s distance from the earth’s center increases by a factor of 3, so its weight decreases by a factor of 32 = 9.

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