A 2.0-N force acts horizontally on a 10-N block that is initially at rest on a horizontal surface. The coefficient of static friction between the block and the surface is 0.50.
19. What is the magnitude of the frictional force that acts on the block?
A) 0 N
B) 2 N
C) 5 N
D) 8 N
E) 10 N
20. Suppose that the block now moves across the surface with constant speed under the action of a horizontal 3.0-N force. Which one of the following statements concerning this situation is false?
A) The block is not accelerated.
B) The net force on the block is zero newtons.
C) The frictional force on the block has magnitude 3.0 N.
D) The coefficient of kinetic friction between the block and the surface is 0.30.
E) The direction of the total force that the surface exerts on the block is vertically upward
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19. B) 2 N
The frictional force is equal to the applied force until the applied force exceeds the maximum static friction force. Since the applied force is 2.0 N, the frictional force is also 2.0 N.
20. D) The coefficient of kinetic friction between the block and the surface is 0.30.
The coefficient of kinetic friction is not given in the problem, so we cannot make any assumptions about its value. The other statements are true: the block is not accelerated (constant speed), the net force is zero (forces are balanced), the frictional force is 3.0 N (equal to the applied force), and the direction of the total force that the surface exerts on the block is vertically upward (normal force).
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