SAT Subject Physics Practice Question 485: Answer and Explanation
A block resting on the surface shown above has a force of 20N applied. Which statement best describes the force between the block and the surface upon which it rests?
A. The normal force is less than 50N.
B. The normal force is greater than 50N.
C. The normal force is equal to 50N.
D. The coefficient of friction increases as the angle increases.
E. The coefficient of friction decreases as the angle increases.
Correct Answer: A
The correct answer is (A). Frictional forces always oppose motion, and when the frictional force in the problem is calculated you must remember to add in the downward part of the 20N force to the normal force.