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The following problem is an example of one of the problem types randomly selected at Work
If you do 231.9 J of work to move a 19.8 kg chair 3.35 m across
the floor at constant velocity, and you are pushing at an angle of 17.9o
relative to the floor, what is the coefficient of kinetic friction between
the floor and the chair?
Suggestions / Method Hints: - draw a free body diagram
- write out the horizontal and vertical force equations... use force*sin(theta) & force*cos(theta) so there is only one force unknown
- you have three unknowns in these two equations - force applied, normal force, coefficient of kinetic friction
- use work=forcehorizontal*distance to obtain a third equation
- you now have three equations & three unknowns - it is now just an algebra problem
- my suggestion... use the work equation to find the horizontal force
- then use the angle to find the magnitude of the force
- your vertical force equation should now tell the value of the normal force
- now use forcehorizontal = forcefiction = coefficient*{normal force}
- solve this last equation for the normal force
Answer: 0.32 List of Problem Hints
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