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State law of conservation of energy and law of conservation of mechanical energy.
Write down the energy transformation taking place
(a) In electric bulb
(b) In torch
(c) In the thermal power station
(d) In solar cell
(e) Electric heater
State the transformation of energy that takes place when
Green plants prepare their food.
Head of a nail hammered hard and it becomes hot.
What is work done by a force of gravity in the following cases?
(a) Satellite moving around the Earth in a circular orbit of radius 35000 km.
(b) A stone of mass 250 g is thrown up through a height of 2.5 m.
How much work is done by a man who tries to push the wall of a house but fails to do so?
If we lift a body of 7 kg vertically upwards to a height of 10 m, calculate the work done in lifting the body.
Establish a relationship between SI unit and commercial unit of energy.
Work done by force acting on an object is equal to the magnitude of the force multiplied by the distance moved in the direction of the force. Work has only magnitude and no direction. Work done is negative when the force acts opposite to the direction of displacement. Work done is positive when the force is in the direction of displacement. The unit of work is newton-metre (N m)or joule (J).
(i) Work done is:
(a) Scalar quantity (b) Vector quantity (c) Tensor quantity (d) None of these
(ii) When force acts against the direction of displacement then work done will be:
(a) positive (b) negative
(c) both a and b can possible (d) None of these
(iii) SI unit of work is:
(a) Joule(J) (b) Newton meter(N-m) (c) both (a) and (b) (d) None of these
(iv) You are lifting stone from floor. Work is done by the force exerted by you on the stone. The object moves upwards. The force you exerted is in the direction of displacement. However, there is the force of gravity acting on the object. Which one of these forces is doing positive work?
Which one is doing negative work?
(v) Define 1 J of work.
Why a man does not do work when he moves on a level road while carrying a box on his head?
Write down the type of energy stored in
(a) spring of a watch
(b) flowing water
(c) rolling stone
(d) raised hammer
(e) running athlete
Define (a) 1 joule (b) 1 watt.
What is the sequence of energy change that takes place in the production of electricity from adam?
Define the following terms.
(a) Work was done (b) Energy (c) Mechanical energy (d) Kinetic energy
(e) Potential energy (f) Power (g) Commercial unit of energy.
Give a reason for the following:
(a) A bullet is released on firing the pistol.
(b) An arrow moves forward when released from the stretched bow.
(c) Winding the spring of a toy car makes it to run on the ground.
(d) Falling water from a dam generates electricity.
(e) Winding the spring of our watch, the hands of the watch movement.