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Class 9 Work and Energy

Illustrate the law of conservation of energy by discussing the energy changes which occur when we draw a pendulum bob to one side and allow it to oscillate. Why does the bob eventually come to rest? What happens to its energy eventually? Is it a violation of the law of conservation of energy?

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A pendulum is a object is hang to a fixed position with thread that do back and forth motion. (left and Right) When bob is on maximum right side ( At Rest ) Since Bob is at some height and at rest not released, so it has stored potential Energy but zero kinetic Energy.Let’s suppose … Read more

Can there be displacement of an object in the absence of any force acting on it? Think. Discuss this question with your friends and teacher.

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Here , we know that Force = Mass * Acceleration When force is 0 , it means Acceleration is also 0. When acceleration is Zero, It means body is moving in uniform motion, since it has speed so it can obviously doing a displacement of an object. Yes , we can say that there be … Read more

What is the work done by the force of gravity on a satellite moving round the earth? Justify your answer.

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Here, When satellite is moving around the earth, the Gravitational force experienced to the satellite along the center of the earth. ( Radius of the Earth ) But the Satellite is moving in circular path along the tangent of the circle. Since displacement is along the tangent. We know the tangent of the circle is … Read more

An object of mass 40 kg is raised to a height of 5 m above the ground. What is its potential energy? If the object is allowed to fall, find its kinetic energy when it is half-way down.

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Here , Mass = 40 kg Height = 5 m g ( force of gravity ) = 10m/sĀ² Potential Energy = Mgh = 40*10*5 = 2000 Joule ( j ) Now Second part when object is at half way down then it gain some velocity now to calculate velocity we have to apply motions of … Read more

Does the transfer of energy take place when you push a huge rock with all your might and fail to move it? Where is the energy you spend going?

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The Rock has huge mass, so friction force is also huge so when we tried to move the rock, our force is much smaller than friction force. According to law of conservation of energy , energy neither created not destroy it can only change to one form to other. so our energy get converted in … Read more

The potential energy of a freely falling object decreases progressively. Does this violate the law of conservation of energy? Why?

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when an object goes to freely falling at some height (h) is has stored potential energy equal to mgh. Then start falling, its height decreases but speed increases so as height decreased we say that potential energy decreased as ( h ) decreased so mgh decreases but on the other hand velocity increases (v) so … Read more

A mass of 10 kg is at a point A on a table. It is moved to a point B. If the line joining A and B is horizontal, what is the work done on the object by the gravitational Force?Explain your answer.

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Here we have to find the work done only by gravitational force. So when an object is moved in horizontal position from Point A to Point B then displacement occurs and gravitation force is acting always downward directing along the earth on the object. So the angle formed between force of gravity and displacement is … Read more