Chapter 10: Work and Energy Case Study Questions | science Class 9 CBSE

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Chapter 10: Work and Energy Case Study Questions | science Class 9 CBSE | ByteNotes.in

Case Study

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Case Set

Case Set 1

Case Analysis

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Ravi pushes a heavy wooden table across a flat floor, applying a continuous force. The table slowly moves in the direction of the push. He is asked to calculate the work done and relate it to energy.

Question 1: Q1. Is Ravi doing work on the table? Why?

Yes, because a force is applied and the table is displaced.
Work is defined as force multiplied by displacement in the same direction.
So work is done according to the scientific definition.

Question 2: Q2. What is the formula to calculate work done?

Work = Force × Displacement
If force and displacement are in the same direction, work is positive.
Unit of work is joule (J).

Question 3: Q3. What does this tell us about energy?

Work done on the object transfers energy to it.
Object gains energy in the form of kinetic or potential energy.
Energy is the capacity to do work.

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Case Set 2

Case Analysis

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A girl lifts her school bag from the floor to her shoulder. Her teacher explains this as an example of work being done against gravity.

Question 1: Q1. What kind of energy increases during lifting?

Gravitational potential energy increases.
It is stored due to change in position.
The higher the lift, the more the energy gained.

Question 2: Q2. What force is acting against the lift?

The girl works against the gravitational pull of Earth.
Gravity resists upward motion of objects.
Force required equals weight (mg) of the object.

Question 3: Q3. How is work related to energy in this case?

Work done on the bag increases its potential energy.
Energy is transferred from the girl to the bag.
This follows the principle of energy conservation.

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Case Set 3

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A boy pushes a wall with all his strength, but the wall does not move. He becomes tired and wonders why his effort isn't considered 'work' in science.

Question 1: Q1. Is scientific work done in this case?

No, because displacement is zero.
Work requires both force and displacement.
Without movement, no work is done scientifically.

Question 2: Q2. Why does he feel tired despite no work?

Energy is spent internally by muscles.
This results in fatigue and heat generation.
But no external mechanical work is recorded.

Question 3: Q3. What does this example demonstrate?

Difference between scientific and common usage of 'work'.
Scientific work needs measurable displacement.
Exertion alone doesn’t guarantee work is done.

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Case Set 4

Case Analysis

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A windmill lifts water from a well using wind energy. Students discuss how this process involves work and energy transformations.

Question 1: Q1. What kind of work is done by the windmill?

It performs mechanical work by lifting water.
A force is applied to displace water upward.
Hence, work is done against gravity.

Question 2: Q2. What is the source of energy here?

The source is wind energy from moving air.
It rotates blades of the windmill.
This mechanical motion powers the pump.

Question 3: Q3. Which energy conversions take place?

Wind energy → Mechanical energy of blades.
Mechanical energy → Potential energy of lifted water.
This is an example of renewable energy usage.

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Case Set 5

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An electric heater is switched on in a room. It converts electric energy into heat, raising the temperature of the room over time.

Question 1: Q1. What kind of energy conversion happens here?

Electrical energy is converted into heat energy.
This is known as the heating effect of electric current.
It occurs due to resistance in the heater coil.

Question 2: Q2. Is work being done in this process?

Yes, as energy is being transferred.
Electricity does work by increasing internal energy of air molecules.
It changes the thermal state of the environment.

Question 3: Q3. What law governs this conversion?

Law of conservation of energy.
Total energy remains the same, just changes form.
Here: Electrical → Thermal energy.

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Chapter sections

Chapter 10: Work and Energy | Case Study Questions

Passage

Question 1: Q1. Is Ravi doing work on the table? Why?

Question 2: Q2. What is the formula to calculate work done?

Question 3: Q3. What does this tell us about energy?

Passage

Question 1: Q1. What kind of energy increases during lifting?

Question 2: Q2. What force is acting against the lift?

Question 3: Q3. How is work related to energy in this case?

Passage

Question 1: Q1. Is scientific work done in this case?

Question 2: Q2. Why does he feel tired despite no work?

Question 3: Q3. What does this example demonstrate?

Passage

Question 1: Q1. What kind of work is done by the windmill?

Question 2: Q2. What is the source of energy here?

Question 3: Q3. Which energy conversions take place?

Passage

Question 1: Q1. What kind of energy conversion happens here?

Question 2: Q2. Is work being done in this process?

Question 3: Q3. What law governs this conversion?

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