Class 9 Science Exploration Solutions English Medium

NCERT Solutions Class 9 Science Exploration English Medium

Work, Energy, and Simple Machines

Topic: Assignments - What Have You Learned?

Chapter 7. Work, Energy, and Simple Machines

This assignment is based on the complete chapter and follows the latest CBSE competency-based assessment pattern. It includes objective, descriptive, application-based, case-study and HOTS questions to strengthen conceptual understanding of work, energy, power and simple machines.

Chapter Assignment

1. One Word Answer

1. The capacity to do work.
2. The SI unit of work.
3. The SI unit of power.
4. Energy possessed due to motion.
5. Energy possessed due to position.
6. The product of force and displacement.
7. The law stating that energy can neither be created nor destroyed.
8. The quantity that measures the rate of doing work.
9. The ratio of load to effort.
10. A device that makes work easier.

2. Fill in the Blanks

1. Work is done only when force produces __________.
2. The SI unit of energy is __________.
3. Work = __________ × Displacement.
4. Kinetic energy depends on mass and __________.
5. The formula of potential energy is __________.
6. Mechanical energy is the sum of __________ and __________.
7. Power = __________ ÷ Time.
8. The SI unit of power is __________.
9. The efficiency of a machine is always __________ than 100%.
10. A pulley is an example of a __________ machine.

3. True or False

1. Pushing a wall without moving it is an example of scientific work.
2. One joule is equal to one newton metre.
3. Potential energy depends upon the height of the object.
4. Kinetic energy becomes zero when an object is at rest.
5. Mechanical energy always remains constant in the absence of friction.
6. Power and energy are the same physical quantities.
7. Simple machines create energy.
8. Mechanical advantage can be greater than one.
9. Efficiency of an ideal machine is 100%.
10. A ramp is an example of an inclined plane.

4. Match the Following

5. Very Short Answer Questions

1. Define work.
2. State the conditions necessary for work to be done.
3. Write the formula for work.
4. Define energy.
5. What is kinetic energy?
6. What is potential energy?
7. State the law of conservation of mechanical energy.
8. Define power.
9. What is a simple machine?
10. Define mechanical advantage.

6. Short Answer Questions

1. Differentiate between positive, negative and zero work with suitable examples.
2. Explain the Work-Energy Theorem.
3. Describe the different forms of energy with examples.
4. Explain kinetic energy and the factors affecting it.
5. Explain potential energy with suitable examples.
6. Describe the conservation of mechanical energy during the free fall of an object.
7. Differentiate between kinetic energy and potential energy.
8. Explain the concept of power and its SI unit.
9. What are simple machines? Explain their importance in daily life.
10. Explain mechanical advantage, velocity ratio and efficiency.

7. Long Answer Questions

1. Explain the concept of work with its conditions, formula, SI unit and real-life applications.
2. Describe the different forms of energy and explain the relationship between work and energy.
3. Explain kinetic energy, potential energy and mechanical energy with suitable examples.
4. State and explain the law of conservation of mechanical energy using the example of a freely falling object.
5. Explain the concept of power and discuss its practical applications.
6. Describe different types of simple machines with suitable examples.
7. Explain mechanical advantage, velocity ratio and efficiency with appropriate diagrams or examples.
8. Discuss the importance of simple machines in transportation, construction and household work.

8. Case Study Questions

Case Study – 1

A worker pushes a heavy box across the floor. The box moves in the direction of the applied force.

1. Is work done in this situation?
2. Which two quantities determine the work done?
3. Write the formula for work.
4. Name the SI unit of work.

Case Study – 2

A ball is thrown vertically upward. It slows down, stops for a moment, and then falls back to the ground.

1. Which type of energy is maximum at the highest point?
2. Which type of energy is maximum just before reaching the ground?
3. Which law explains this change of energy?
4. What happens to the total mechanical energy (ignoring friction)?

Case Study – 3

A student climbs a staircase carrying a school bag to the first floor.

1. Which type of energy increases?
2. Has work been done? Give a reason.
3. Which force acts against the motion?
4. State the formula for potential energy.

Case Study – 4

A mechanic uses a pulley to lift a heavy engine.

1. Which simple machine is used?
2. Why is a pulley useful?
3. Define mechanical advantage.
4. Why is the efficiency of a practical machine less than 100%?

Case Study – 5

Two students lift the same object to the same height. One student takes less time than the other.

1. Did both students perform the same amount of work?
2. Which student produced greater power?
3. Define power.
4. Write its SI unit.

9. Competency-Based Questions

1. Why is no scientific work done while pushing a wall that does not move?
2. Explain why a fast-moving car possesses more kinetic energy than a slow-moving car.
3. Why does water stored in a dam have potential energy?
4. How does a roller coaster demonstrate the conservation of mechanical energy?
5. Why is power an important factor in selecting machines?
6. Explain why the efficiency of practical machines is always less than 100%.
7. How does an inclined plane reduce human effort?
8. Why do engineers use pulleys and levers in construction work?
9. Explain the energy transformations that occur in a hydroelectric power station.
10. Give two examples from daily life where simple machines make work easier.

10. HOTS Questions

1. A person carries a heavy suitcase on a horizontal road. Under what condition is scientific work considered zero? Explain.
2. Two objects have the same mass, but one moves twice as fast as the other. Compare their kinetic energies.
3. Why does the total mechanical energy remain constant during free fall even though kinetic and potential energies keep changing?
4. Can a machine reduce the total work done? Justify your answer.
5. Why is a longer ramp easier to use than lifting a load vertically?
6. Explain why a powerful motor can complete the same work in less time.
7. How would daily life be affected if simple machines did not exist?
8. A machine has a high mechanical advantage but low efficiency. Explain how this is possible.
9. Give one real-life example where energy changes through more than two forms before performing useful work.
10. Why are work, energy and power considered closely related physical quantities? Explain with suitable examples.

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