Question

In which of the following does the work done by a body against friction always result in?
${\text{A}}{\text{.}}$ Loss of kinetic energy
${\text{B}}{\text{.}}$ Loss of potential energy
${\text{C}}{\text{.}}$ Gain of kinetic energy
${\text{D}}{\text{.}}$ Gain of potential energy

Answer 1

Hint: Here, we will proceed by defining the term work widely used in physics. Then, we will define the frictional force. Finally, we will discuss the effect of the frictional force on the motion of the body on which it is acting.

Complete Step-by-Step solution:
Work is the measure of the transfer of energy that takes place when an object is moved over a distance by an external force of which at least part is applied in the direction of the displacement. If the force is constant, work can be computed by multiplying the path length by the force component that acts along the path.
Mathematically, the work W is equal to the force F times the distance d i.e., W = Fd
If the force is being exerted at an angle $\theta $ to the displacement, the work done is given by the formula
W= ${\text{Fd}}\cos \theta $
Friction is a force that acts between two sliding surfaces, or surfaces that attempts to slide over each other. For example, friction makes this difficult when you're trying to move a book along the floor.
Friction always works in the opposite direction to the direction the object moves, or attempts to move in. A moving object is often slowed down by friction.
The amount of friction depends on the materials which make up the two surfaces. The rougher the surface, the greater the amount of friction produced. Friction also yields heat. If you quickly rub your hands together you'll feel that they're getting warmer.
Friction can be a useful force because as we walk, it prevents our feet from sliding onto the pavement and keeps car tyres from skidding down the lane. When you walk, there's friction between the tread on the shoes and the ground. This friction is effective at grasping the ground and preventing sliding.
Friction also stands in contrast to motion. A body does work at the expense of its kinetic energy against friction. Hence, the work done by a body against friction always results in loss of kinetic energy.
Therefore, the work done by a body against friction always results in loss of kinetic energy.
Hence, option A is correct.

Note- The kinetic energy of a body having mass m and moving with velocity v is equal to $\dfrac{1}{2}{\text{m}}{{\text{v}}^2}$. From this relation, it is clear that if the velocity of motion of a body is decreasing due to the friction then the kinetic energy of that body will also be decreasing because kinetic energy is directly proportional to the square of the velocity.