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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?
- 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 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.
- A certain Household has consumed 250 units of energy during a month. How much energy is this in Joules?
- 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?
- The potential energy of a freely falling object decreases progressively. Does this violate the law of conservation of energy? Why?
- 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 its velocity from 5 m sā1 to 2 m sā1. Calculate the work done by the force.
- A battery lights a bulb. Describe the energy changes involved in the process.