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What is the power output of a machine that raises a load of 750 N through a height of 16 m in 5 seconds?
What is the power output of a machine that raises a load of 750 N through a height of 16 m in 5 seconds?
If a motor has a power of 40 kW, what speed can it raise a load of 20,000 N?
If a motor has a power of 40 kW, what speed can it raise a load of 20,000 N?
How much work is done by a boy moving against a friction force of 5 N after travelling a distance of 1.5 km and additional distances?
How much work is done by a boy moving against a friction force of 5 N after travelling a distance of 1.5 km and additional distances?
What is the electric energy consumed by a 1200 W iron used for 30 minutes daily in April?
What is the electric energy consumed by a 1200 W iron used for 30 minutes daily in April?
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Calculate the equivalent power of an engine that pumps 2000 tonnes of water from a height of 20 m in a minute.
Calculate the equivalent power of an engine that pumps 2000 tonnes of water from a height of 20 m in a minute.
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What is the speed of car B after car A collides with it and comes to rest?
What is the speed of car B after car A collides with it and comes to rest?
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How much work is done on a trolley of mass 5 kg given an initial velocity of 4 m/s over a distance of 16 m?
How much work is done on a trolley of mass 5 kg given an initial velocity of 4 m/s over a distance of 16 m?
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What force in newtons does a 150 kg car engine exert when moving at a speed of 20 m/s with a power output of 500 W/kg?
What force in newtons does a 150 kg car engine exert when moving at a speed of 20 m/s with a power output of 500 W/kg?
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If a person can jump 0.4 m high on Earth, how high can he jump on a planet where his weight is about half?
If a person can jump 0.4 m high on Earth, how high can he jump on a planet where his weight is about half?
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A ball dropped from a height of 10 m reduces its energy by 40% after striking the ground. How high can it bounce back?
A ball dropped from a height of 10 m reduces its energy by 40% after striking the ground. How high can it bounce back?
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What is the power required for an electric iron used for 30 minutes at 1200 W?
What is the power required for an electric iron used for 30 minutes at 1200 W?
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What is the efficiency of a machine that does work of 1.323 × 10^7 J in 600 seconds?
What is the efficiency of a machine that does work of 1.323 × 10^7 J in 600 seconds?
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A girl having a mass of 35 kg sits on a trolley of 5 kg. How much work does she do?
A girl having a mass of 35 kg sits on a trolley of 5 kg. How much work does she do?
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What is the total mechanical energy of a freely falling body at point C just before it strikes the ground?
What is the total mechanical energy of a freely falling body at point C just before it strikes the ground?
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In the scenario where a light object and a heavy object have the same momentum, which object has the greater kinetic energy?
In the scenario where a light object and a heavy object have the same momentum, which object has the greater kinetic energy?
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How much work do the men do while holding a 250 kg box without moving it?
How much work do the men do while holding a 250 kg box without moving it?
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If a car is traveling at a steady speed of 30 m/s against a resistive force of 2000 N, how much energy is used in 1 second?
If a car is traveling at a steady speed of 30 m/s against a resistive force of 2000 N, how much energy is used in 1 second?
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What is the gravitational potential energy increase when a 36 kg package is raised by 2.4 m?
What is the gravitational potential energy increase when a 36 kg package is raised by 2.4 m?
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What happens to the operation of a conveyor belt if a package with a mass greater than 36 kg is raised through a height of 2.4 m?
What happens to the operation of a conveyor belt if a package with a mass greater than 36 kg is raised through a height of 2.4 m?
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What type of energy is primarily utilized by the car engine to drive the vehicle?
What type of energy is primarily utilized by the car engine to drive the vehicle?
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How much is the minimum power that the car engine has to deliver to maintain speed while overcoming a resistive force of 2000 N?
How much is the minimum power that the car engine has to deliver to maintain speed while overcoming a resistive force of 2000 N?
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What happens to the kinetic energy when the velocity of a vehicle of mass 500 kg increases from 36 km/h to 72 km/h?
What happens to the kinetic energy when the velocity of a vehicle of mass 500 kg increases from 36 km/h to 72 km/h?
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What is the work done in lifting a mass of 200 kg through a vertical distance of 6 m against gravity?
What is the work done in lifting a mass of 200 kg through a vertical distance of 6 m against gravity?
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Which formula correctly expresses kinetic energy for a moving body with mass m and velocity v?
Which formula correctly expresses kinetic energy for a moving body with mass m and velocity v?
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What is required for a person to feel tired while holding a 250 kg box, even when doing no mechanical work?
What is required for a person to feel tired while holding a 250 kg box, even when doing no mechanical work?
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If a man of mass 60 kg runs up a flight of 30 steps each 20 cm high in 15 seconds, what is the power developed?
If a man of mass 60 kg runs up a flight of 30 steps each 20 cm high in 15 seconds, what is the power developed?
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What is the ratio of the initial kinetic energy to the final kinetic energy when the velocity of the rocket is suddenly tripled?
What is the ratio of the initial kinetic energy to the final kinetic energy when the velocity of the rocket is suddenly tripled?
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Which of the following describes the power produced by Avinash and Kapil correctly?
Which of the following describes the power produced by Avinash and Kapil correctly?
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When a constant force is applied to increase the velocity of a body, what does this force accomplish?
When a constant force is applied to increase the velocity of a body, what does this force accomplish?
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During the pole-vault performance, which energy type is primarily transformed to potential energy as the athlete rises?
During the pole-vault performance, which energy type is primarily transformed to potential energy as the athlete rises?
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What is the gravitational potential energy change for a hammer of mass 2.0 kg dropped from a height of 4.8 m?
What is the gravitational potential energy change for a hammer of mass 2.0 kg dropped from a height of 4.8 m?
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What is the work done by the force of gravity on an object that returns to the same height?
What is the work done by the force of gravity on an object that returns to the same height?
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How is the total mechanical energy of a freely falling body calculated?
How is the total mechanical energy of a freely falling body calculated?
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What energy transformation takes place when a hammer drops and hits the ground?
What energy transformation takes place when a hammer drops and hits the ground?
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Which of the following correctly defines gravitational potential energy?
Which of the following correctly defines gravitational potential energy?
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When comparing power and energy between Anil and Ashok, what can be concluded?
When comparing power and energy between Anil and Ashok, what can be concluded?
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What is the work done on a mass 'm' raised to a height 'h' against gravity?
What is the work done on a mass 'm' raised to a height 'h' against gravity?
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What happens to the kinetic energy of an object as it falls freely under gravity?
What happens to the kinetic energy of an object as it falls freely under gravity?
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What kind of energy is primarily involved when the pole is bent during the vault?
What kind of energy is primarily involved when the pole is bent during the vault?
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If a workman lifts a hammer weighing 520 N up 3.0 m in 5.0 s, what is the useful power exerted by his legs?
If a workman lifts a hammer weighing 520 N up 3.0 m in 5.0 s, what is the useful power exerted by his legs?
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Study Notes
Work, Power, and Energy - Class 9 Extra Questions
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Work: Work is done when a force acts on an object and the object is displaced.
- Conditions for Work: A force must act, and the object must move.
- Positive Work: Force acts in the direction of motion (e.g., pulling a lawn roller forward).
- Zero Work: Force is perpendicular to the direction of motion (e.g., a porter carrying a load).
- Negative Work: Force acts opposite to the direction of motion (e.g., work done against friction).
- Calculating Work: Work (W) = Force (F) × Displacement (s) × cos(θ), where θ is the angle between force and displacement.
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Energy: The capacity of a body to do work. Units are Joules (J) and Kilojoules (kJ).
- Source of Energy for Life Processes: Food.
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Kinetic Energy (KE): Energy of motion.
- Units: Joules (J)
- Relationship with Speed: KE ∝ v² (Kinetic energy is proportional to the square of velocity). Doubling the speed quadruples the kinetic energy.
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Potential Energy (PE): Stored energy due to position or shape.
- Gravitational Potential Energy: Energy due to position (PE = mgh, where m=mass, g=gravity on Earth, h=height).
- Elastic Potential Energy: Energy stored in a stretched or compressed object (e.g., a spring).
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Law of Conservation of Energy: Energy can neither be created nor destroyed, only transformed from one form to another (verified experimentally by James Prescott Joule).
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Power: Rate of doing work. Unit is Watts (W) or Kilowatts (kW). Power = (Work / Time).
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Commercial unit of Energy: Kilowatt-hour (kWh) ; 1 kWh = 3.6 × 106 J.
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Converting Forms of Energy:
- Electricity to light/heat (e.g., electric heater)
- Mechanical to electrical (e.g., dynamo)
- Heat to mechanical (e.g., steam engine)
- Mechanical to electrical (e.g., hydroelectric power plant)
- Chemical to electrical (e.g., battery)
Additional Notes
- Work done by a constant force is zero when the object does not move (displacement = 0).
- Constant velocity means net force (and hence work done) is zero.
- Potential energy doesn't change if there's no change in height on a level surface.
- Kinetic Energy depends on mass and square of velocity: KE =1/2 * m*v^2.
Differences
- Moment of a force causes rotational motion. Work done causes translational motion.
- Power measures the rate of doing work.
- Energy measures the capacity to do work.
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