(a) Heat energy produced in the engine into K.E. of the car.
(b) Electric energy into potential energy
(c) Electric energy into mechanical energy
(d) P.E. into K.E.
(e) Electrical energy into heat and light.
(f) Electrical energy into sound energy.
(g) Chemical energy into heat energy and light.

(i) Electric heater. Electrical energy into heat.
(ii) Electric motor.Electrical energy into mechanical energy
(iii) Dynamo. mechanical energy into electrical energy
(iv) Electric cell. Chemical energy into electrical energy.
(v) Headphone. Electrical energy into sound.
(vi) Hydroelectric power station Mechanical energy into electrical energy
(vii) Steam engine. Heat into mechanical energy
(viii) Solar battery. Solar energy into electrical energy
(ix) Photoelectric cell. Light energy into electrical energy.

Work is said to be done whenever a force a acts on a body moves in the direction of the force.
Two conditions need to be satisfied for work to be done.These are as follows:
(i) A force should act on the body.
(ii) The body must be displaced in the direction of the applied force.
If either of the above two conditions is not satisfied, then work is not done.
Examples: We give below some situations from daily life in which work is done.
(i) Push a pebble lying on a surface.The pebble moves through some distance.Here we apply a force on the pebble and the pebble gets displaced.So, we have done work on the pebble.
(ii) We apply a force to lift a book through a height.The book rises up.We have done work in moving up the book.
(iii) A bullock is pulling a cart.The cart moves.There is a force on the cart and the cart has moved.The bullock has done work on the cart.

Here, m = 40 kg, g = 10 ms^-2, h = 5m
Potential energy of the object at a height of 5m,
E_p = mgh =40 x 10 x 5= 2000J
When the object is half-way down, let its velocity be v.Then
v²- u² = 2gs
v² - 0² = 2 x 10 x 2.5 or v² = 50
Kinetic energy of the object, E_k=1/2 x 40 x 50 = 1000 J

m = 20 kg, u = 5 ms^-1, v = 2 ms^-1
Work done=Change in K.E.
W = 1/2 mv²-1/2mu² = 1/2m(v²-u²)
= 1/2 x 20(2²-5²) = 10 (4-25) = - 10 x 21
= - 210 J
The negative sign indicates the retarding nature of the applied force.

(i) Energy consumed by a 100 W bulb each day
= 100 W x 2 h=200 Wh = 200/1000 = 0.2 kWh
Energy consumed by five 40 W tubes each day
= 5 x 40 W x 4 h = 800 Wh = 800/1000 = 0.8 kWh.
Total energy consumed each day
= 5 x 40 W x 4 h = 800 Wh = 800/1000 = 0.8 kWh
Total energy consumed each day = 0.2 + 0.8 = 1.0 kWh
Total energy consumed in 60 days = 1.0 x 60 = 60 kWh
(ii) Cost of 1 kWh =  Rs. 3
Cost of 60 kWh = 3 x 60 =  Rs.180

Energy of a body is defined as its capacity or ability to do work.When a body is capable of doing more work, it is said to possess more enrgy.
Examples:
(i) When a fast moving cricket ball hits a stationary wicket, it throws away the wicket.The moving ball possess energy and hence does work on the wicket.
(ii) A hammer raised through a certain height possesses energy.When it falls on a nail placed on a piece of wood, it drives the nail into the wood.
(iii) When a child winds a toy car and does work in moving against the force of friction.
In all the above examples, the objects acquire capability of doing work through different means and these objects are said to possess energy.

Here m = 1000 kg, u=30 m/s, v = 0, s = 50 m
v² - u² = 2as
0-30² = 2a.50 or a = -900/100 = -9 m/s²
Deceleration=  9m/s²
decelerating force, F = ma =1000 x 9 = 9000 N
Work done by the brakes, W = F.s = 9000 x 50J = 450000J

Given, power, P = 2 W, time, t = 1min = 60 s
Total work, W = Pt
= 2 x 60s = 120J
\(\therefore\) 1.5 J work is done in 1 beat.
\(\therefore\) 120 J work will be done in \(\frac{1\times 120}{1.5}\) = 80 beats
Therefore,number of beatsper min = 80.

No, he is not doing any work. It is because, there is no
motion in the man.
W = F's = F x 0 = 0      [\(\therefore\) s = 0] (1+1)

Zero.When the satellite moves around the earth, the force of gravity acts on it along the radius of its orbit while its direction of motion is along the tangent to the orbit at any point. Thus, force acts perpendicular to displacement.Hence, the work done on the satellite is zero.

Let the mass of each body be m.
K.E. of the first body, K₁ = 1/2m(2v)²
K.E. of the second body, K₂ = 1/2m(3v)²
Ratio of the kinetic energies=K₁/K₂ = 1/2m.4v² /1/2m.9v² = 4/9 = 4:9 

Velocity of the boy, v = Velocity of car = 54km/hour = 54 x 1000 m/3600 s = 15 m/s
Mass of the boy, m = 40 kg
K.E. of the boy = 1/2mv² = 1/2 x 40 x (15)² = 4500J

(i) First the battery converts chemical energy into electrical energy. Then the bulb converts this electrical energy into heat and light.
(ii) Here, m = 500 kg, v = 0 and
u = 36 kmh^-1  = \(\frac{36\times 1000}{3600}\) = 10 ms^-1
\(\therefore\) Work done = Change in kinetic energy
= \(\frac{1}{2}m(v^2-u^2)=\frac{1}{2}\times 500(0-10^2)\)
= \(\frac{1}{2}\times 500\times 100\) = - 25000 Js^-1
So, it is negative because work is done to stop the car.