# Forms of energy

Question 1 Calculate the kinetic energy of a body of mass 2 Kg moving with a velocity of 0.1 m/s?

Question 2 How much work should be done on a bicycle of mass 20Kg to increase its speed from 2m/s to 5m/s?

Question 3 What are the various forms of energy?

Question 4 What do you understand by kinetic energy of a body?

Question 5 Write an expression for the kinetic energy of a body of mass m moving with velocity v?

Question 6 How does kinetic energy depends on its mass and velocity?

Question 7 If the speed of a body is halved,what will be the change in its kinetic energy?

Question 8 A ball of mass 200g falls from a height of 5 m.What is its kinetic energy when it just reaches the ground?

Question 9 Find the momentum of a body of mass 100 g having kinetic energy of 20J?

Question 10 What is the kinetic energy of a body of mass 1 kg moving with speed of 2m/s?

Question 11 What is potential energy?

Question 12 Is potential energy a scalar quantity or vector quantity?

Question 13 On what factors does the potential energy of a body depends?

Question 14 Give example where body possesses kinetic energy?

Question 15 What happens to the potential energy when height is doubled?

Question 16 A body of mass 2 Kg is thrown vertically upwards with an initial velocity of 20m/s.What will be its potential energy at the end of 2sec?

__Forms of Energy__

Kinetic energy,Potential energy,Chemical energy,Heat energy,Light energy,Sound energy,Electrical energy,Nuclear energy.

**Kinetic Energy**

The energy of a body due to its motion is called **kinetic energy.**

Ex:1)A moving cricket ball can do work in pushing back the stamps.

2)Moving water can do work in turning the turbine for generating electricity.

3)Moving wind can do work in turning the blades of wind mill.

4)A moving hammer drives a nail into wood because of its kinetic energy.

5)A moving bullet can penetrate even a steel plate.

6)A moving bus,car,falling stone possesses kinetic energy.

7)A falling coconut,running athlete possesses kinetic energy.

The kinetic energy of a moving body is measured by the amount of work it can do before coming to rest.

The kinetic energy of a body moving with a certain velocity is equal to the work done on it to make it acquire that velocity.

Let us consider an object of mass m,moving with a uniform velocity u.Let it be displaced through a distance S.

When a constant force F acts on it in direction of its displacement.

Work Done= Force* Distance

W=F*S

The work done on the object will cause a change in its velocity.Let its velocity changes from u to v.Let a be the acceleration produced.

The relation connecting the initial velocity(u) and final velocity(v) of an object moving with a uniform acceleration(a) and displacement,S,is

v^{2} – u^{2 } =2aS

v^{2} – u^{2 }

———- = S

2a

From Newton’s Second law of motion

F= m*a

F

a=—-

m

v^{2} – u^{2 } m

———- * —– = S

2 F

W=F *S

W= m (v^{2} – u^{2 })

————

2

If the object is starting from its stationary position ie u=0,then

1

W=— m v^{2}

2

1

Kinetic energy= —– m v^{2}

2

Thus,kinetic energy possessed by an object of mass m,and moving with uniform velocity,v, is

1

KE = —– m v^{2}

2

Kinetic energy is directly proportional to mass of body and square of velocity of body.

If mass of a body is doubled,its kinetic energy also gets doubled and if mass of body is halved,its kinetic energy al get halved.

If the velocity of body is doubled,its kinetic energy,becomes four times.

If the velocity of body is halved,then its kinetic energy becomes one-forth.

Heavy bodies moving with high velocities have more kinetic energy than slow moving bodies of small mass.

__Potential Energy__

A brick lying on the ground.It has no energy so it cannot do any work.

Let us lift this brick to the roof of a house.Some work has been done in lifting this brick against the force of gravity.This work gets stored up in the brick in the form of potential energy.

The energy of a brick lying on the roof of a house is due to its higher position wrt ground.

Elastic potential energy is due to change in the shape of body.It can be brought about by compressing,bending or twisting.some work has to be done to change the shape of a body.

The energy of a body due to its position or change in shape is called **potential energy.**

When you stretch a rubber band,energy transferred to band is its potential energy.

An object increases its energy when raised through a height.This is because work is done on it against gravity while is is being raised.The energy present in such an object is the **Gravitational Potential energy**.

Consider an object of mass m.Let it be raised through a height h,from the ground.The minimum force required to raise the object is equal to the weight of the object mg.The work done on the object against gravity will be

Work=Force*Displacement

W=F*h

W=mg*h

W=mgh

This work done by gravity depends on the difference in vertical heights of initial and final position of object and not on the path along which object is moved.