A block of wood is pulled by a horizontal string across a rough surface at a constant velocity with a force of 20 N.The coefficient of kinetic friction between the surfaces is 0.3.The force of friction is
A)impossible to determine without knowing the mass of the block.
B)impossible to determine without knowing the speed of the block.
C)0.3 N
D)6 N
E)20 N

Question

Quizplus · Accepted Answer

Since the block moves at a constant velocity, the force of friction must equal the pulling force, which is 20 N, to satisfy Newton's first law of motion.

A Block of Wood Is Pulled by a Horizontal String