MCAT Physics Question 65: Answer and Explanation
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Question: 65
5. A positive charge of +Q is fixed at point R a distance d away from another positive charge of +2Q fixed at point S. Point A is located midway between the charges, and point B is a distance 
from +2Q, as shown below. In which direction will a positive charge move if placed at point A and point B, respectively?
- A. Toward the +Q charge for both
- B. Toward the +2Q charge for both
- C. Toward the +Q charge at point A, and toward the right at point B
- D. Toward the +2Q charge at point A, and toward the right at point B
Correct Answer: C
Explanation:
A positive charge placed at A will experience two forces: a force to the left due to +2Q and a force to the right due to +Q. Because point A is the same distance from +Q and +2Q, the force due to +2Q will be larger than that due to +Q, and there will be a net force to the left (toward +Q). At point B, the forces from both +Q and +2Q will point to the right, so there will be a net force to the right.