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

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Answer:

No, it does not violate the law of conservation of energy here. The reason is that there is a proportional and equal relationship between potential energy and kinetic energy. That is, the total energy of the object is always conserved.

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Two objects of different masses falling freely near the surface of Moon from same height would

A freely falling object eventually stops on reaching the ground. What happens to its kinetic energy?

Soni says that the acceleration in an object could be zero even when several forces are acting on it. Do you agree with her? Why?

In each of the following a force F is acting on an object of mass m. The direction of the displacement is from west to east shown by the longer arrow, observe the diagrams carefully and state whether the work done by the force is negative, positive or zero.

Calculate the work required to be done to stop a car 1500 kg moving at a velocity of 60 km/h?

An object of mass m is moving with a constant velocity v. How much work should be done on the object in order to bring the object to rest?

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?

An electric heater is rated 1500 W. How much energy does it use in 10 hours?

A person holds a bundle of hay over his head for 30 minutes and gets tired. Has he done some work or not? Justify your answer.

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.

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

An object of 40 kg in raised to a height of 5m 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. (g = 10 ms–2)

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?

What are the various energy transformations that occur when you are riding a bicycle?

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.

Certain force acting on a 20 kg mass changes it's velocity from 5 ms–1 to 2 ms–1. Calculate the work done by the force.

A battery lights a bulb. Describe the energy change involved in the process.

An object thrown at a certain angle to the ground moves in a curved path and fall back to the ground. The initial and the final points of the path of the object lie on the same horizontal line. What is the work done by the force of gravity on the object.

Look at the activities listed below. Reason out whether or not work is done in the light of your understanding of the term "work". Suma is swimming in a pond. A donkey is carrying a load on its back. A windmill is lifting water from a well. A green plant is carrying out photosynthesis. An engine is pulling a train. Food grains are getting dried in the sun. A sailboat is moving due to wind energy.

Chapter 10 NCERT Class 9 Science SOLUTIONS

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Chapter 10 NCERT Class 9 Science SOLUTIONS

Question:

Answer:

More NCERT Questions

Two objects of different masses falling freely near the surface of Moon from same height would

A freely falling object eventually stops on reaching the ground. What happens to its kinetic energy?

Soni says that the acceleration in an object could be zero even when several forces are acting on it. Do you agree with her? Why?

In each of the following a force F is acting on an object of mass m. The direction of the displacement is from west to east shown by the longer arrow, observe the diagrams carefully and state whether the work done by the force is negative, positive or zero.

Calculate the work required to be done to stop a car 1500 kg moving at a velocity of 60 km/h?

An object of mass m is moving with a constant velocity v. How much work should be done on the object in order to bring the object to rest?

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?

An electric heater is rated 1500 W. How much energy does it use in 10 hours?

A person holds a bundle of hay over his head for 30 minutes and gets tired. Has he done some work or not? Justify your answer.

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.

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

An object of 40 kg in raised to a height of 5m 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. (g = 10 ms–2)

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?

What are the various energy transformations that occur when you are riding a bicycle?

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.

Certain force acting on a 20 kg mass changes it's velocity from 5 ms–1 to 2 ms–1. Calculate the work done by the force.

A battery lights a bulb. Describe the energy change involved in the process.

An object thrown at a certain angle to the ground moves in a curved path and fall back to the ground. The initial and the final points of the path of the object lie on the same horizontal line. What is the work done by the force of gravity on the object.

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