Chapter: 7 – Work, Energy, and Simple Machines
Maximum Marks: 50
Suggested Time: 1 Hour 30 Minutes

This Class 9 Science Exploration Chapter 7 Sample Paper 1 is designed to help students practise important concepts from “Work, Energy, and Simple Machines.” The paper covers work, conditions for work, energy, kinetic and potential energy, conservation of energy, power, mechanical advantage, efficiency, and simple machines. Complete solutions are provided at the end for self-assessment and revision.

Sample Paper 1

General Instructions

1. All questions are compulsory.
2. Read each question carefully.
3. Show all steps in numerical problems.
4. Use SI units wherever applicable.
5. Draw neat and labelled diagrams wherever required.
6. Take g=10 m/s2, unless otherwise stated.

Section A — Objective Questions

10 × 1 = 10 Marks

Q1. Work is said to be done on an object when:

a) A force acts on it but there is no displacement
b) There is displacement in the direction of the applied force
c) The object has mass
d) The object is at rest

Q2. The SI unit of work is:

a) Newton
b) Watt
c) Joule
d) Pascal

Q3. Which of the following is a form of mechanical energy?

a) Kinetic energy
b) Sound energy only
c) Chemical energy only
d) Electrical energy only

Q4. The energy possessed by an object due to its motion is called:

a) Potential energy
b) Kinetic energy
c) Chemical energy
d) Thermal energy

Q5. The energy possessed by an object due to its position or configuration is called:

a) Kinetic energy
b) Potential energy
c) Sound energy
d) Electrical energy

Q6. Power is defined as:

a) Work × time
b) Work ÷ time
c) Force × time
d) Energy × distance

Q7. The SI unit of power is:

a) Joule
b) Newton
c) Watt
d) Metre

Q8. Which simple machine consists of a wheel with a rope or chain passing around it?

a) Lever
b) Pulley
c) Inclined plane
d) Screw

Q9. A machine that helps us to lift a load by applying force over a greater distance is used mainly to:

a) Create energy
b) Make work easier
c) Increase mass
d) Destroy energy

Q10. According to the law of conservation of energy:

a) Energy can be created but not destroyed
b) Energy can be destroyed but not created
c) Energy can neither be created nor destroyed
d) Energy disappears when work is done

Section B — Very Short Answer Questions

5 × 2 = 10 Marks

Q11. Define work. State the two basic conditions necessary for work to be done.

Q12. Differentiate between kinetic energy and potential energy.

Q13. What is power? Write its SI unit.

Q14. State the law of conservation of energy.

Q15. What is a simple machine? Give two examples.

Section C — Short Answer and Numerical Questions

4 × 3 = 12 Marks

Q16. A force of 25 N moves an object through a distance of 4 m in the direction of the force. Calculate the work done.

Q17. Explain why no mechanical work is done when a person pushes a rigid wall but the wall does not move.

Q18. Calculate the kinetic energy of a body of mass 4 kg moving with a velocity of 5 m/s.

Q19. Explain the difference between work and power. Give one example to show that two people can do the same amount of work but have different powers.

Section D — Application-Based and Numerical Questions

2 × 4 = 8 Marks

Q20. A stone of mass 2 kg is lifted vertically to a height of 5 m.

Answer the following:

a) What type of energy does the stone gain?
b) Calculate the gain in potential energy.
c) What happens to its potential energy if its height is doubled?
d) What happens to its potential energy if its mass is doubled while height remains unchanged?

Q21. A machine is used to lift a load of 600 N by applying an effort of 150 N.

a) Identify the load.
b) Identify the effort.
c) Calculate the mechanical advantage of the machine.
d) What does the mechanical advantage tell us?

Section E — Long Answer and Numerical Questions

2 × 5 = 10 Marks

Q22. Explain the principle of conservation of energy using the example of an object falling from a height. Describe how its potential and kinetic energies change during the fall.

Q23. A student pushes a box with a constant force of 80 N and moves it through a distance of 6 m in 12 seconds.

Calculate:

a) Work done on the box.
b) Power developed by the student.
c) Write the SI units of work and power.

SOLUTIONS

Section A — Answers

Q1. b) There is displacement in the direction of the applied force

Q2. c) Joule

Q3. a) Kinetic energy

Q4. b) Kinetic energy

Q5. b) Potential energy

Q6. b) Work ÷ time

Q7. c) Watt

Q8. b) Pulley

Q9. b) Make work easier

Q10. c) Energy can neither be created nor destroyed

Section B — Solutions

Q11. Work

Work is said to be done when a force acting on an object produces displacement in the direction of the force.

The two basic conditions are:

1. A force must act on the object.
2. The object must undergo displacement having a component in the direction of the force.

For a force acting along the direction of displacement: W=Fs

Q12. Kinetic and Potential Energy

Kinetic energy: KE=21​mv2

Gravitational potential energy: PE=mgh

Q13. Power

Power is the rate at which work is done. P=tW​

where W is work done and t is time taken.

The SI unit of power is the watt (W).

Q14. Conservation of Energy

The law of conservation of energy states that energy can neither be created nor destroyed. It can only be transformed from one form to another.

The total energy of an isolated system remains constant.

Q15. Simple Machine

A simple machine is a device that helps us perform work more conveniently by changing the magnitude or direction of the applied force.

Examples include:

• Lever
• Pulley
• Inclined plane
• Wheel and axle
• Screw
• Wedge

Section C — Solutions

Q16. Work Done

Given: F=25 N s=4 m

Since force and displacement are in the same direction: W=Fs W=25×4 W=100 J​

Answer: The work done is 100 J.

Q17. Pushing a Rigid Wall

When a person pushes a rigid wall, a force is applied to the wall.

However, the wall does not move, so its displacement is: s=0

Therefore: W=Fs W=F×0 W=0​

Thus, no mechanical work is done on the wall because there is no displacement.

Q18. Kinetic Energy

Given: m=4 kg v=5 m/s

Formula: KE=21​mv2

Substituting: KE=21​×4×52 KE=2×25 KE=50 J​

Answer: The kinetic energy is 50 J.

Q19. Work and Power

Work measures the amount of energy transferred when a force causes displacement. W=Fs

Power measures how quickly the work is done. P=tW​

For example, suppose two students each lift the same load through the same height. They perform the same amount of work.

If Student A takes 10 seconds and Student B takes 20 seconds, Student A has greater power because the same work is completed in less time.

Section D — Solutions

Q20. Stone Lifted to a Height

Given: m=2 kg h=5 m g=10 m/s2

a) Type of energy gained

When the stone is lifted to a height, it gains gravitational potential energy.

b) Gain in potential energy

PE=mgh PE=2×10×5 PE=100 J​

c) If height is doubled

Potential energy is: PE=mgh

Therefore, potential energy is directly proportional to height.

If height is doubled, potential energy also becomes double.

New PE: 200 J​

d) If mass is doubled

Potential energy is also directly proportional to mass.

Therefore, if mass is doubled while height remains unchanged, potential energy becomes double.

Q21. Mechanical Advantage

Given:

Load: L=600 N

Effort: E=150 N

a) Load

The load is the resistance or object being lifted: 600 N​

b) Effort

The effort is the force applied to the machine: 150 N​

c) Mechanical Advantage

MA=EffortLoad​ MA=150600​ MA=4​

d) Meaning

A mechanical advantage of 4 means that the machine allows a 600 N load to be lifted with an effort of 150 N, under the given conditions.

Section E — Solutions

Q22. Conservation of Energy During Falling

Consider an object held at a certain height above the ground.

At the initial position

The object has maximum gravitational potential energy because it is at its greatest height.

Its kinetic energy is zero if it starts from rest.

During the fall

As the object falls, its height decreases. Therefore, its potential energy decreases.

At the same time, its speed increases, so its kinetic energy increases.

Thus: Potential Energy→Kinetic Energy

Just before reaching the ground

The object’s potential energy is at its minimum relative to the ground, while its kinetic energy is at its maximum.

If air resistance is ignored: Total Mechanical Energy remains constant​

Therefore, the decrease in potential energy is equal to the increase in kinetic energy.

This demonstrates the law of conservation of energy: energy changes from one form to another but is not destroyed.

Q23. Work and Power

Given: F=80 N s=6 m t=12 s

a) Work Done

Since force and displacement are in the same direction: W=Fs W=80×6 W=480 J​

b) Power

Power is: P=tW​

Substitute: P=12480​ P=40 W​

c) SI Units

• Work: Joule (J)
• Power: Watt (W)

Final Answers

Work done = 480 J

Power = 40 W