Physlet Illustration: Work Done by Friction

 

 

 
F = Newtons µk=  

 
A block of mass 50 kg is being pulled across a rough floor by a constant, horizontal force, as shown. It starts from rest, and its velocity is shown in m/s. You can adjust the coefficient of kinetic friction (0.1 < µk< 0.5) and/or the pulling force (0 N < F < 1000 N). The graph shows the work done by the pulling force as well as the block's kinetic energy as functions of the block's position. What is the difference between the two? Can you verify it quantitatively?

Hints

  1. In addition to the pulling force, what other force does work on the block?
  2. Is this additional work positive or negative?
  3. How large is the force of friction between the block and the floor?
  4. Pause the animation at some point, and calculate the block's kinetic energy at that instant.
  5. How far has the block moved by this time?
  6. How much work has been done by the pulling force?
  7. How much work has been done by the frictional force?

Reference

See Walker, Section 8-4

Illustration written by Steve Mellema and Chuck Niederriter