(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.

(a) Positive Work. Work done by a force is positive if the force acts in the direction of displacement.Then
\(W=F\times s\times cos\ 0°=F\ s\)
Examples:
(i) When a body falls freely under gravity, the work done by the force of gravity is positive.
(ii) When a horse pulls a cart, the applied force and displacement are in the same direction, the work done by the horse is positive.
(b) Negative Work. Work done by a force is negative if the force acts opposite to the direction of displacement.Then
\(W=F\times s\times cos\ 180°=F\ s(-1)=-F\ s\)
Examples:
(i) When a body is lifted up, the work done by the gravitational force is negative.This is because the gravitational acts vertically downwards while the displacement is in the vertically upward direction.
(ii) When brakes are applied to a moving vehicle, the work done by the braking forces is negative.The braking force acts in the backward direction while the displacement of the vehicle is in the forward direction.

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.

(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

Here m = 25 kg, h = 10m, g = 10m/s²
(a) Work done = mgh =25 x 10 x 10J = 2500J
(b) Gravitational P.E.= Work done  =2500J
(c) Gravitational P.E. at a height of 30m = 25 x 30 x 10J = 7500J
P.E. at 30 m height/P.E. at 10m height = 7500J/2500J = 3
Thus, P.E. increases by 3 times.
(d) K.E. of the body will be maximum just before the body strikes the ground.

(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.