A 95 kg clock initially at rest on a horizontal floor requires a 650 N horizontal force to set it in motion.
After the clock is in motion, a horizontal force of 560N
keeps it moving with a constant speed. Find Msand uk
between the clock and the floor.

You are given that the mass of the clock M is 95 kg.

This is true whether the clock is in motion or not.

Fs is the frictional force required to keep the clock from moving.

Thus Fk = uk W = uk M g      the force required to move clock at constant speed.     (the kinetic frictional force)

uk = 560 N / 931 N = .644   since the weight of the clock is 931 N  (95 * 9.8)

us  is the frictional force requited to start the clock moving

us = static frictional force = 650 / 931 -= .698

the answer is 100. i just did this lesson and got a 100% on it. : )

-fishtank