A block is pushed across a rough horizontal surface from point A to point B by a force (magnitude P = 5.4 N)as shown in the figure.The magnitude of the force of friction acting on the block between A and B is 1.2 N and points A and B are 0.5 m apart.If the kinetic energies of the block at A and B are 4.0 J and 5.6 J,respectively,how much work is done on the block by the force P between A and B?
A)2.7 J
B)1.0 J
C)2.2 J
D)1.6 J
E)3.2 J

Question

A block is pushed across a rough horizontal surface from point A to point B by a force (magnitude P = 5.4 N)as shown in the figure.The magnitude of the force of friction acting on the block between A and B is 1.2 N and points A and B are 0.5 m apart.If the kinetic energies of the block at A and B are 4.0 J and 5.6 J,respectively,how much work is done on the block by the force P between A and B? 
A)2.7 J 
B)1.0 J 
C)2.2 J 
D)1.6 J 
E)3.2 J

Quizplus · Accepted Answer

The work done on an object is equal to the change in its kinetic energy, which is given as:
Work done = Change in kinetic energy = Kinetic energy at B - Kinetic energy at A = 5.6 J - 4.0 J = 1.6 J
However, this work is done against two forces - the applied force P and the force of friction. We know that the work done by friction is given as:
Work done by friction = Force of friction x Distance = 1.2 N x 0.5 m = 0.6 J
Therefore, the total work done by the applied force P is:
Total work done = Work done - Work done by friction = 1.6 J - 0.6 J = 1.0 J
Hence, the correct answer is option C.

A Block Is Pushed Across a Rough Horizontal Surface from Point