PHYSICS [2 Mark Question Answer]

Displacement, s = 10 m
Force, F = 120 N
Work done, W = ?
We know that,
W = F x s = 120 N x 10 m
= 1200 Nm or 1200 J

Force, F = 80 N
Displacement, s = 5 m Work done, W = ?
Work done, W = F x s = 80 x 5 = 400 Nm or 400 J

When a man with a suitcase held in his hand climbs a staircase, he is applying force against the gravity, to raise it to a height. The suitcase has been displaced because of the force applied. Therefore, work is said to be done.

When a man is walking holding a suitcase, the suitcase moves. But the force applied (force of gravity) on the suitcase is in the vertically upward direction (against the gravity), whereas the displacement is in the horizontal direction on platform. A vertical force can never cause a horizontal displacement. So the displacement of the suitcase is not due to the force acting on it. Therefore, no work is done.

Force, F = 45 N
Displacement, s = 0.5 m Work done, W = ?
We know that,
W = F x s = 45 x 0.5 Nm = 22.5 Nm or 22.5 J

Displacement and force applied are directly proportional to the work done. Greater the magnitude of force applied, more is the work done. Greater is the displacement, more is the work done.

The sources of energy that do not get depleted on use and can be used again and again are called renewable sources of energy. Examples : The sun, wind and water are renewable resources of energy.

Wind is moving air which possesses kinetic energy. This energy is used by windmills to turn the shafts of generators to generate electricity.

Kinetic energy of a body is the energy possessed by it due to its motion or movement. Examples : A child riding a bicycle, a moving bus, moving air (wind), flowing water – all possess kinetic energy.

There are three factors responsible for work to be done by a body:

• A force must be applied on the body.
• The body should move from its position of rest.That is, there should be a displacement, or there should be a change in the shape or size of the object.
• The displacement must be because of the force applied.

Series of energy transformations is called as energy chain. In a water cycle, the heat energy of the sun evaporates water from water bodies. After evaporation, this water forms clouds and the clouds brings rains. The mechanical energy of water has been caused due to solar energy (heat energy of sun).

According to the law of conservation of energy, energy can neither be created nor destroyed. It can be transformed
converted from one form to another. When a car engine runs, the chemical energy of the fuel changes into kinetic energy, heat energy and sound energy.

Potential energy is the energy possessed by a body due to its position or height of the body. Water stored in a dam has potential energy because work is done to raise the water to a certain height against the pull of gravity. The is acquired as potential energy.