MCAT Physics Question 48: Answer and Explanation
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Question: 48
3. Two wooden balls of equal volume but different density are held beneath the surface of a container of water. Ball A has a density of
and ball B has a density of
When the balls are released, they will accelerate upward to the surface. What is the relationship between the acceleration of ball A and that of ball B?
- A. Ball A has the greater acceleration.
- B. Ball B has the greater acceleration.
- C. Balls A and B have the same acceleration.
- D. It cannot be determined from information given.
Correct Answer: A
Explanation:
Using Newton's second law, Fnet = ma, we obtain the following equation:
Fbuoy ? mg = ma
Thus,
Both balls experience the same buoyant force because they are in the same liquid and have the same volume (Fbuoy = ρVg). Thus, the ball with the smaller mass experiences the greater acceleration. Because both balls have the same volume, the ball with the smaller density has the smaller mass (m = ρV), which is ball A.