A hand pushes a 2 kg block along a table from point A to point C as shown in the

Question

A hand pushes a 2 kg block along a table from point A to point C as shown in the figure below. The table has been prepared so that the left half of the table (from A to B) is frictionless. The right half (from B to C) has a non-zero coefficient of friction equal to . The hand pushes the block the full distance from A to C using a constant force of 7 N. The block starts off at rest at point A and comes to a stop when it reaches point C. The distance from A to B is 0.5 m and the distance from B to C is also 0.5 m.

A. From A to B:
1) The work done by the weight force is  ( positive , negative , zero )
2) The work done by the normal force is  ( positive , negative , zero )
3) The work done by the pushing force is  ( positive , negative , zero )
4) The change in kinetic energy of the block is  ( positive , negative , zero )

B. From B to C:
1) The work done by the weight force is ( positive , negative , zero )
2) The work done by the normal force is   ( positive , negative , zero )
3) The work done by the pushing force is  ( positive , negative , zero )
4) The work done by the friction force is  ( positive , negative , zero )
5) The change in kinetic energy of the block is  ( positive , negative , zero )
6) The magnitude (absolute value) of the work done by the friction force is ( greater than , less than , equal to ) the magnitude (absolute value) of the work done by the pushing force.

Explanation / Answer

Ans A) 1,2since weight force and normal force act perpendicular to displacment so work done by them is 0

3 pushing force act in direction of displacement so work done is positive

4) since work done is positive so change in kinetic energy is positive

B) 1,2since weight force and normal force act perpendicular to displacment so work done by them is 0

3 pushing force act in direction of displacement so work done is positive

4)friction force act opposite to direction of displacement so work done by friction is negative

5)since block finally stop at c so change in kinetic energy is negative

6) The magnitude (absolute value) of the work done by the friction force is greater than the magnitude (absolute value) of the work done by the pushing force since the object come to rest at point c friction force has to be greater than pushing force otherwise block would not stop at point c

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