Work and Energy Test - 9

When an object starts to fall freely, the K.E. increase with decrease in potential energy and total mechanical energy remains constant.  So, statement A, C, and D are incorrect  and B is correct.

At a height h/2 PE = mg (h/2) = 1/2 mgh
The rest (1/2 mgh) of the PE is converted into K.E.
Thus, at a height (h/2), PE = KE = 1/2 mgh

When we rub our hands against each other they become warm. Here, heat is generated due to the loss of kinetic energy of the hands due to friction. Thus, heat is a form of energy that can be produced when some form of energy is lost. In this example, kinetic energy is converted into heat energy.

The head of a nail hammered into the wooden plank by speed the K.E. is converted into heat energy. So, the head of a nail hammered into the wooden plank becomes hot.

Levers do not create energy. Levers convert a small force applied over a long distance to a large force applied over a small distance. Work is the force times the distance, W = Fd, so the total work done is the same with or without the lever. Muscular energy is present in the muscle of animals. Lever transforms mechanical energy into muscular energy is false statement.

According to the law of conservation of energy, energy neither be created nor be destroyed, it can be transformed from one form to another. Total energy in the universe always remains constant.

Initial velocity (u)= 0,
Final velocity (v) =10 m/s,

V² – u² = 2gh
(10)² – (0)² = 2 × 10 × h
100 = 20 h
h = 100/20

h = 5m.

(A) Mechanical energy is not always conserved. Mechanical energy is the sum of kinetic and potential energy in a system. Mechanical energy is conserved so long as we ignore air resistance, friction, etc. When we don't ignore outside forces, such as those just mentioned, mechanical energy is not conserved.
(B) According to law of conservation of energy the total energy of the system is always conserved.
So, Statement B is true stamen and Statement A is false statement.

(1) In Battery, chemical energy converts into electrical energy.
(2) In Bulb, electrical energy converts into light energy.
(3) In Steam engine, steam energy converts into mechanical energy.
(4) In microphone,  sound energy converts into electrical energy.

When a satellite moves around the Earth along a circular path, then the force of gravity acts on it towards the centre. The force of gravity of the earth and the direction of movement of the satellite are perpendicular to each other means θ = 90° .
Therefore W= F x S cos θ. (cos 90° = 0)
 W = 0J.