A student pulls a wooden box along a rough horizontal floor at constant speed by means of a force P as shown to the right. Which of the following must be true?
Correct answer: A. P > fand N < W
- A. P > fand N < W
- B. P > f and N = W
- C. P = f and N > W
- D. P = f and N = W
Explanation
The correct answer is that P > f and N < W. The force P is applied at an upward angle, which means it has both horizontal and vertical components. The vertical component of P reduces the normal force, making it less than the weight, W. The horizontal component of P must be greater than the frictional force, f, to maintain constant speed. The other options are incorrect because they either disregard the influence of the vertical component of P or misinterpret the relationship between P, f, and N.
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