Physics students study a piano being pulled across a room on a rug. They know that when it is at rest, it experiences a gravitational force of 2200 N. When it is being pulled with 1200 N it is sliding across the room in equilibrium, but the students feel like they had to pull harder than 1200 N at first to begin motion.
Answer
A
The static and kinetic frictional forces are equal, so the static frictional force is equal to 1200 N.
B
The kinetic frictional force is greater than the static frictional force, so the kinetic frictional force is greater than 1200 N.
C
The static frictional force is greater than the kinetic frictional force, so the static frictional force is greater than 1200 N.
D
The static and kinetic friction are both equal to the gravitational force of 2200 N.