Question

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.

Answer 1

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