A 14.0 kg block is dragged over a rough,horizontal surface by a 91.0 N forceacti

Question

A 14.0 kg block is dragged over a rough,horizontal surface by a 91.0 N forceacting at 20.0° above the horizontal. The block is displaced5.00 m, and the coefficient of kineticfriction is 0.300.

(a) Find the work done on the block by the 91.0 N force.

(b) Find the work done on the block by the normal force.

(c) Find the work done on the block by the gravitational force.

(d) What is increase in internal energy of the block-surface systemdue to friction?

(e) Find the total change in the block's kinetic energy.

Explanation / Answer

   W = FScos
   = (91)(5) cos20
   =427.56J
The work done by the normal force is zero as normal force isperpendicular to the displacement.
Work done due to gravity is also zero. because =90.
Increase in internal energy
   Wf = mgS
   =0.3(14)(9.8)(5)
   = 205.8J
The net work done is
   Wnet = 427.56-205.8
     = 221.76
This work is equal to change in kinetic energy of theblock.

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