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(d) electricity

If the demand for energy is more than 1 the supply then it leads to energy crisis.

In a mechanical clock the spring is compressed by winding, it attains potential energy. The releasing of the spring slowly is the kinetic energy, using that the wheels of the clock turns, therefore potential energy is converted into kinetic energy. PE → KE → mechanical energy.

In the quartz clock, the electric cell gives, the electrical energy and it is converted into mechanical energy by which the wheels of the clock turns. Therefore the energy transformation is chemical energy → electrical energy → mechanical energy.

The bus has greater kinetic energy since it has got greater mass than car. even though they are moving with the same speed.

1. electric bulb 

2. motor 

3. electric heater 

4. microphone 

5. electric cell

The two forms of mechanical energy are 

1. Potential energy and 

2. Kinetic energy

The energy which a body possess either due to its position or due to its deformation is called potential energy. PE = m × g × h Potential energy of a body depends on 

1. the mass of a body and 

2. the height to which it is raised from ground.

m = 200 grams 

= 0.2 kg 

h = 5 m u 

= 0 v = 7 

 v² -u² = 2gh 

v²– 0² = 2 x 9.8 x 5 

v² = 98 

kinetic energy, KE = \(\frac{1}{2}mv^2\)

\(\frac{1}{2} \times \frac{200}{1000}\) x 98 

= 9.8 joule

The moving air, the moving ball, the flowing water, the moving Striker.

The energy possessed a body by virtue of its motion is called kinetic energy. KE = 1/2 mv² 

Kinetic energy depends on 

1. the mass of the body and 

2. velocity with which it is moving

1. potential energy 

2. potential energy 

3. kinetic energy 

4. potential energy 

5. potential energy 

6. potential energy

True The energy of a flying kite is kinetic energy.

False The energy stored in the water of a dam is the potential energy.

(a) True

(b) False

(c) True

(d) True

(e) False.

(f) False

Correct — There is always some loss of energy in conversion from one form of energy to the other form, so the total energy is conserved.

(g) True

(a) An electric fan converts electrical energy into mechanical energy. 

(b) Cooking gas converts chemical energy into heat energy. 

(c) Energy possessed by a compressed spring is potential energy. 

(d) The ability to do work is called energy 

(e) The energy possessed by a body due to its position is called potential energy. 

(f) The energy possessed by a body due to its motion is called kinetic energy. 

(g) Green plants convert light energy into chemical energy. 

(h) The S.I.unit of energy is joule 

(i) An object falling freely from the roof of a multistorey building has potential energy and kinetic energy when halfway down the building

(a) Work is said to be done by a forte only when the body moves.

(b) Work done = Force × distance moved in direction of force.

(c) The energy of a body is its capacity to do work.

(d) The S.I. unit of energy is joule.

(e) The potential energy of a body is due to its state of rest or position and kinetic energy of body is due to its state of motion.

(f) Gravitational potential energy U = mass × force of gravity on unit mass × height.

(g) Kinetic energy = 1/2 × mass × (speed)²

(h) Power P = work done/time taken.

(i) The S . i. unit of power is watt

(j) 1 H.P. = 746 W

The S.I. unit of work is joule.

No work is done by a force if the body does not move.

True Power spent by a body depends on the time for which it does work.

Two coolies A and B do some work in time 1 minute and 2 minute respectively. The power spent is more by coolie A than by B

The expression of power P is P = F × d/t

(i) Potential energy to kinetic energy. 

(ii) Chemical energy of coal changes to heat energy of the steam. Heat energy changes into mechanical energy. 

(iii) Chemical energy into light and heat energy. 

(iv) Electrical energy change into mechanical energy.

1 H.P. Is equal to 1 W

1. chemical energy

1. Both work and energy have the same units

When a boy doubles his speed, his kinetic energy becomes four times.

(a) AMOVING BALL due to motion possesses KINETIC ENERGY.

(b) A stone at rest on the top of a building possesses POTENTIAL ENERGY, 

∴ Due to height above ground.

(c) A compressed spring possesses potential energy due to changed position of spring.

(d) A moving bus possesses kinetic energy due to motion.

(e) A bullet fired from a gun possesses kinetic energy due to motion.

(f) WATER FLOWING IN A RIVER possesses kinetic energy due to its motion.

(g) A STRETCHED RUBBER BAND possesses potential energy due to changed position.

The different forms of energy are : 

(i) Mechanical energy 

(ii) Heat energy 

(iii) Light energy 

(iv) Chemical energy 

(v) Sound energy 

(vi) Magnetic energy 

(vii) Electrical energy and 

(viii) Atomic energy or nuclear energy.

F= 10 kgf = 10 × 10N= 100 N,

Displacement S = 0.5 m

Work done

(i) When displacement is in the direction of force

W = F × S

W= 100 × 0.5 = 50 J

Energy spent = w = 4 × 10⁵ J Time

taken = 10 s

Power = Energy / Time

P = 4 x 10⁵/10 = 4 x 10⁴ W

S.I. unit of work is Joule

Joule “is that much work done when a force of 1N displaces the body through a distance of lm in the direction of force.”

The energy is measured in the same unit as work. Therefore the S.I. unit of energy is joule (symbol J). 

A body is said to possess an energy of one joule if a force of 1 newton moves the body by a distance of 1 metre in the direction of force. 

Another unit of energy is calorie (symbol cal) where 1 cal = 4.2 J. A bigger unit is kilo-calorie (symbol kcal) where 1 kcal = 1000 cal.

Two factors are :

(i) Magnitude of force applied (F).

(ii) Distance moved by the body in the direction of force (d)

Energy is the capacity of doing work.

ENERGY: “Capacity of doing work” is called ENERGY

KINETIC ENERGY: “The energy possessed by a body by virtue of its motion is called KINETIC ENERGY.” 

Example : A bullet moving at high speed through has small mass, possesses kinetic energy and can penetrate the body. 

Or 

When a stretched bow is released the potential energy of arrow changes into kinetic energy and makes the arrow to move.

The S.I. unit of energy is Joule(J)

Joule “is the capacity of a body to work of 1 J irrespective of time taken.”

RELATION BETWEEN WORK AND ENERGY: “Energy is the capacity of doing work” Every form of energy → is work.

i.e. work done on body is STORED IN THE FORM OF ENERGY. ENERGY is spent when a body does work.

Thus to do more amount of work-more energy is needed.

The mechanical energy is found in two forms namely : 

(a) The potential energy, and 

(b) The kinetic energy.

Two KINDS OF MECHANICAL ENERGY :

(i) The Potential energy (P.E.)

(ii) The Kinetic energy (K.E.)

POTENTIAL ENERGY : (P.E. or U)

“The energy possessed by a body due its position above the ground . or change in state.”

UNIT : Unit of P.E. = S.I. UNIT OF ENERGY = Joule (J)

The energy of a body at rest is called the potential energy. It is defined as follows : Potential energy of a body is the energy possessed by it due to its state of rest or position. Actually, it is the work spent in bringing the body to that state of rest or position. 

It is written as P.E. or U. 

The S.I. unit of potential energy is Joules.

(i) Potential energy of a body is the energy possessed by it due to its state of rest or position. It is the energy stored when work is done on the body to bring it to that state or position. 

(ii) Potential energy of a body in the raised (or lifted) position depends on two factors : 

(1) the mass of the body greater the mass of the body, greater is the potential energy of the body), and 

(2) the height of the body above the ground (greater the height of the body, greater is its potential energy.)

The potential energy of a body in the raised position depends upon the following two factors : 

(a) The mass of the body: Greater the mass of the body, greater is the potential energy of the body. 

(b) Its height above the ground : Higher the height of the body, greater is its potential.

The body B having mass 20 kg has the greater potential energy. This can be explained as follows :

 P.E. = mgh . 

For both the bodies gravity and height are same so the body with greater mass possesses greater potential energy.

As ‘g’ is constant in both cases and quantity of water (m) is the same in both cases potential energy depends on height. Since the height of the second bucket kept on the second floor is greater. Hence, the second bucket on the second floor has greater P.E.

A bucket full of water kept on second floor has the greater potential energy. This can be explained as follows : 

P.E. = mgh 

Mass of both bucket and the gravitational force are same, so the body at greater height will possess more potential energy.