Practice this TNPSC Physics Energy Test 2 to improve your conceptual knowledge and prepare confidently for TNPSC Group 2, Group 2A, and Group 4 examinations. This test covered important concepts related to Work, Power and Mechanical Energy, including positive work, negative work, zero work, factors affecting work done, power comparison, horsepower, efficiency, input and output work, useful energy, and the relationship between work and energy. These questions are designed in TNPSC exam style to strengthen conceptual understanding and practical application of energy-related topics.
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TNPSC Physics Energy Test 2 – All Questions Detailed Explanations
In TNPSC Physics Energy Test 2, each question is explained with clear and exam-oriented concepts to help you understand the correct answer. These explanations strengthen your knowledge of TNPSC Energy Questions and improve your performance in TNPSC Physics Quiz practice for TNPSC Group 2, Group 2A, and Group 4 examinations.
1. Negative work is done by a force when:
Answer: B. Force acts opposite to the direction of displacement
A force does negative work when it acts in the direction opposite to the displacement of an object. In such cases, the force opposes the motion and reduces the object’s kinetic energy. Friction and braking force are common examples of forces that perform negative work.
Quick Revision
- Force opposite to displacement → Negative work
- Reduces the object’s motion
- Example: Friction, brakes
Real-Life Example
When a cyclist applies the brakes, the braking force acts opposite to the bicycle’s motion and performs negative work, slowing it down.
2. Which of the following is the best example of zero work done by a force?
Answer: C. A person pushing a wall that does not move
Work is done only when a force causes displacement. If an object does not move despite the application of force, the displacement is zero, and therefore the work done is also zero.
Quick Revision
- No displacement → Zero work
- Force alone cannot produce work
- Both force and displacement are required
Real-Life Example
Trying to push a heavy wall without moving it requires effort, but no work is done in the scientific sense.
3. A porter carries a suitcase on his head while walking along a horizontal road. The work done by the upward force exerted by the porter is:
Answer: C. Zero
The porter applies an upward force to support the suitcase, while the suitcase moves horizontally. Since the force and displacement are perpendicular (90°), the work done by the upward force is zero.
Quick Revision
- Force perpendicular to displacement → Zero work
- Angle between force and displacement = 90°
- Common TNPSC conceptual question
Real-Life Example
A waiter carrying a tray horizontally performs zero work on the tray by the upward supporting force.
4. Which factor does NOT affect the work done by a constant force?
Answer: D. Colour of the object
The work done by a constant force depends on the magnitude of the force, the displacement of the object, and the angle between the force and displacement. The colour of the object has no effect on the amount of work done.
Quick Revision
- Work depends on force, displacement and direction
- Colour has no physical role
- SI unit of work: Joule (J)
Real-Life Example
Whether a box is red or blue, the work required to push it the same distance remains unchanged.
5. Two workers perform the same amount of work. One completes it in 5 minutes and the other in 10 minutes. The first worker has:
Answer: B. Greater power
Power is the rate at which work is done. When the same amount of work is completed in less time, the power produced is greater. Therefore, the worker who finishes the task in 5 minutes has higher power.
Quick Revision
- Power = Work ÷ Time
- Same work + Less time = Greater power
- SI unit of power: Watt (W)
Real-Life Example
Two people climb the same staircase. The person who reaches the top first produces greater power because the same work is completed in less time.
6. Horsepower is commonly used to express the power of:
Answer: C. Engines and motors
Horsepower (HP) is a unit used to measure the power output of engines and motors. Although the SI unit of power is the watt (W), horsepower is still widely used in automobiles, pumps, tractors, and other machinery to indicate engine performance.
Quick Revision
- Horsepower measures power.
- Commonly used for engines and motors.
- 1 Horsepower ≈ 746 Watts.
Real-Life Example
The power of a car or motorcycle engine is often specified in horsepower, such as 100 HP or 150 HP.
7. A machine receives 500 J of input energy and delivers 400 J of useful output energy. Its efficiency is:
Answer: C. 80%
Efficiency is the ratio of useful output energy to input energy, expressed as a percentage. Here, Efficiency = (400 J ÷ 500 J) × 100 = 80%. A higher efficiency means less energy is wasted.
Quick Revision
- Efficiency = (Useful Output ÷ Input) × 100
- Efficiency is expressed as a percentage.
- No machine is 100% efficient.
Real-Life Example
An electric motor that converts most of the supplied electrical energy into mechanical energy has high efficiency.
8. The useful work obtained from a machine is known as:
Answer: B. Output work
Output work is the useful work performed by a machine after converting the supplied input energy. Due to friction and other energy losses, the output work is always less than or equal to the input work.
Quick Revision
- Useful work = Output work.
- Input work is supplied to the machine.
- Output work is always less than or equal to input work.
Real-Life Example
A crane uses electrical energy to lift heavy loads. The lifting of the load represents the machine’s output work.
9. Which statement correctly explains the relationship between work and energy?
Answer: B. Energy is the capacity to do work.
Energy is defined as the capacity to perform work. Whenever work is done, energy is transferred from one object or system to another. Both work and energy have the same SI unit, the joule (J).
Quick Revision
- Energy is the capacity to do work.
- Work transfers energy.
- SI unit of both work and energy: Joule (J).
Real-Life Example
A fully charged battery stores electrical energy, which is used to perform work when it powers a device like a flashlight.
10. An efficient machine is one that:
Answer: C. Converts most of the input energy into useful output
An efficient machine converts a large portion of the input energy into useful output while minimizing energy losses due to friction, heat, and sound. Higher efficiency means better performance and reduced energy wastage.
Quick Revision
- Efficient machines reduce energy loss.
- Useful output is maximum.
- Efficiency can never exceed 100%.
Real-Life Example
Modern inverter air conditioners are more efficient because they use more of the supplied electrical energy for cooling and waste less energy.
11. Which of the following situations involves positive work done by gravity?
Answer: C. A ripe fruit falls freely from a tree.
Gravity does positive work when an object moves in the same direction as the gravitational force. As the fruit falls downward, both the force of gravity and the displacement act in the same direction, resulting in positive work.
Quick Revision
- Force and displacement in the same direction → Positive work.
- Gravity does positive work during free fall.
- Increases the object’s kinetic energy.
Real-Life Example
A coconut falling from a tree gains speed because gravity performs positive work on it.
12. Which statement is correct regarding the efficiency of a machine?
Answer: B. Efficiency is always less than or equal to 100%.
Efficiency is the percentage of input energy converted into useful output energy. Since some energy is always lost as heat, sound, or friction, no machine can have an efficiency greater than 100%.
Quick Revision
- Efficiency ≤ 100%.
- Some energy is always lost.
- Friction is the main cause of energy loss.
Real-Life Example
An electric mixer converts most electrical energy into mechanical energy, but some energy is lost as heat and sound.
13. Which one of the following activities requires the greatest power?
Answer: A. Climbing 20 steps in 15 seconds.
Power is the rate of doing work. When the same amount of work is completed in less time, more power is produced. Therefore, climbing the steps in the shortest time requires the greatest power.
Quick Revision
- Power = Work ÷ Time.
- Same work + Less time = Greater power.
- SI unit of power: Watt (W).
Real-Life Example
An athlete running up a staircase quickly produces more power than someone climbing slowly.
14. Consider the following statements:
- Work can be done only when force causes displacement.
- If displacement is zero, the work done is zero.
Answer: C. Both 1 and 2
Work is done only when an applied force causes displacement of an object. If there is no displacement, the work done remains zero regardless of the amount of force applied.
Quick Revision
- Force and displacement are both necessary.
- No displacement → No work.
- Work depends on both force and displacement.
Real-Life Example
Pushing a stationary truck without moving it does not result in any work being done.
15. A machine has an efficiency of 75%. The remaining 25% of the input energy is mainly:
Answer: C. Lost as heat, sound and friction.
Machines cannot convert all the supplied energy into useful work. A portion of the input energy is always lost due to friction between moving parts, heat generation, and sound production, reducing the machine’s overall efficiency.
Quick Revision
- Energy losses occur due to friction, heat and sound.
- Higher efficiency means lower energy loss.
- No practical machine is 100% efficient.
Real-Life Example
A motorcycle engine becomes hot during operation because some of the fuel energy is lost as heat instead of being converted into useful mechanical work.
16. Which of the following statements best distinguishes work from power?
Answer: B. Power measures the rate of doing work.
Work is the energy transferred when a force causes displacement, whereas power indicates how quickly that work is done. Two people may perform the same amount of work, but the one who completes it in less time produces greater power.
Quick Revision
- Work = Force × Displacement.
- Power = Work ÷ Time.
- SI unit of power: Watt (W).
Real-Life Example
Two workers lift identical loads to the same height. The worker who finishes first develops greater power.
17. A person pushes a box with a constant force, but the box does not move due to friction. The work done on the box is:
Answer: C. Zero
Even though a force is applied, the box does not move because friction prevents displacement. Since displacement is zero, the work done on the box is also zero.
Quick Revision
- Work requires displacement.
- No displacement → Zero work.
- Force alone cannot produce work.
Real-Life Example
Trying to push a parked car without moving it requires effort, but no work is done on the car.
18. Which of the following devices is generally rated in horsepower instead of watts?
Answer: C. Diesel engine
Horsepower is a traditional unit used to express the power of engines and heavy machinery. Although watts are the SI unit of power, engine performance is commonly specified in horsepower.
Quick Revision
- Horsepower is used for engines.
- 1 Horsepower ≈ 746 Watts.
- Watt is the SI unit of power.
Real-Life Example
The engine capacity of a tractor is often described as 50 HP or 75 HP rather than in watts.
19. Which of the following statements correctly explains why no machine is 100% efficient?
Answer: B. A part of the input energy is always lost due to friction and other factors.
Every machine experiences energy losses due to friction, heat, sound, and vibration. As a result, only a part of the supplied energy is converted into useful work, making 100% efficiency impossible in practical machines.
Quick Revision
- Energy losses are unavoidable.
- Friction is the major cause of reduced efficiency.
- Efficiency is always less than or equal to 100%.
Real-Life Example
An electric motor becomes warm during operation because some electrical energy is lost as heat.
20. Which one of the following is the most suitable example of converting electrical energy into mechanical energy?
Answer: A. An electric fan rotating its blades
An electric fan uses electrical energy supplied from the mains to rotate its blades through an electric motor. This is a direct conversion of electrical energy into mechanical energy.
Quick Revision
- Electrical energy → Mechanical energy.
- Electric motors perform this energy conversion.
- Common examples: Fans, mixers, water pumps.
Real-Life Example
A water pump uses an electric motor to convert electrical energy into mechanical energy, enabling it to lift and transport water.
Further Reading:
To improve your understanding after completing TNPSC Physics Energy Test 2, explore NCERT Class 9 Science – Work, Energy and Power. These official resources provide a strong foundation for TNPSC Energy Questions and help you build concepts for future TNPSC Physics Quiz practice.
Official NCERT Textbook: Chapter 7 – Work, Energy and Power
