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Super TET Science: Work, Power and Energy Practice Questions

Revision session covering the concepts, units, and formulas of Work, Power, and Energy for teaching exams. Explains the differences between kinetic, potential, and mechanical energy with real-life examples and calculations. Reviews dimensional formulas, energy transformations, and conservation theorems through practice questions.

Teaching
Physics
English · 8 topics
Checked against the video on 25 Oct 2026

Made by AI from the YouTube video UP SUPERTET SCIENCE Class-7 | कार्य, सामर्थ्य और ऊर्जा | 50 MCQ | उ.प्र. प्राथमिक शिक्षक भर्ती 2026 (opens YouTube in a new tab) by Balaji Study Adda, then checked against it. All credit for the teaching goes to the creator. Tap a topic’s time to confirm a fact in the video.

Super TET Science: Work, Power and Energy Practice Questions

English8 topics · 7 MCQs · 12 flashcardsWatch the video (opens YouTube in a new tab)

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In short

Revision session covering the concepts, units, and formulas of Work, Power, and Energy for teaching exams. Explains the differences between kinetic, potential, and mechanical energy with real-life examples and calculations. Reviews dimensional formulas, energy transformations, and conservation theorems through practice questions.

Fundamental Units of Work, Power, and Energy

Work has the SI unit of Joule (J), where 1 Joule equals 1 Newton multiplied by 1 Meter.
Must knowWork is a scalar quantity having magnitude only and no direction.
Power has the SI unit of Watt (W), defined as 1 Joule per second.
1 Horsepower (HP) equals 746 Watts, commonly used to rate heavy machinery.
Energy also has the SI unit of Joule, representing the capacity to do work.
In the CGS system, the unit for both work and energy is the Erg.

Work Calculations, Angle Dependence, and Unit Conversions

Work done is calculated using the formula W = F × d × cos(θ).
Must knowWhen the angle between force and displacement is 90 degrees, the work done is zero because cos(90°) = 0.
- A porter carrying a load on his head and moving horizontally does zero work against gravity.
1 Joule is equal to 10⁷ Ergs, converting from the MKS system to the CGS system.
1 Newton in force corresponds to 10⁵ Dynes in the CGS system.
Must know1 kilowatt-hour (kWh) is equal to 3.6 × 10⁶ Joules and represents 1 commercial electric unit.

Kinetic and Potential Energy Formulas and Dynamics

Kinetic energy (K.E.) is given by the formula (1/2) × m × v², where m is mass and v is velocity.
Must knowKinetic energy is always positive and can never be negative.
Gravitational potential energy (P.E.) equals m × g × h, where g is acceleration due to gravity and h is height.
At the surface of the Earth where height h = 0, gravitational potential energy is taken as zero.
If the velocity of an object is doubled, its kinetic energy becomes four times because kinetic energy is proportional to the square of velocity.
If the velocity of an object is halved, its kinetic energy reduces to one-fourth.

Mechanical Energy and Everyday Energy Forms

Mechanical energy is the sum of kinetic energy and potential energy.
In the absence of friction, the total mechanical energy of an object remains conserved.
The coiled spring of a wound-up clock stores elastic potential energy, which gradually converts to kinetic energy to turn the clock hands.
Flowing water possesses kinetic energy due to its velocity, which rotates turbines in hydroelectric power stations.
Power is defined as the rate of doing work (P = W / t), and machines are rated by their power output.
Energy is defined as the total capacity to do work; power depends on time, whereas energy is concerned with total work done.

Work Signs, Electrical Devices, and Energy Transformations

When force and displacement are in the same direction (θ = 0°), work done is maximum and positive.
- Gravity does positive work on an object falling freely downwards.
When force and displacement are in opposite directions (θ = 180°), work done is negative because cos(180°) = -1.
- The force of friction does negative work when brakes are applied to a vehicle.
An electric motor converts electrical energy into mechanical energy and functions based on Fleming's left-hand rule.
A dynamo (generator) operates on the principle of electromagnetic induction to convert mechanical energy into electrical energy.
A microphone converts sound energy into electrical signals as sound vibrates its diaphragm.
A loudspeaker converts electrical signals back into sound energy, acting opposite to a microphone.

Device	Input Energy	Output Energy
Electric Motor	Electrical Energy	Mechanical Energy
Dynamo	Mechanical Energy	Electrical Energy
Microphone	Sound Energy	Electrical Energy
Loudspeaker	Electrical Energy	Sound Energy
Solar Cell	Solar/Light Energy	Electrical Energy
Candle Burning	Chemical Energy	Light and Heat Energy
Battery/Cell	Chemical Energy	Electrical Energy

Momentum, Falling Bodies, and Conservation of Energy

Kinetic energy in terms of momentum (p) is expressed by K.E. = p² / (2m).
Doubling the momentum of an object increases its kinetic energy to four times.
Momentum (p = m × v) is a vector quantity.
A flying bird or an aeroplane possesses both kinetic and potential energy simultaneously.
A stretched bowstring holds potential energy, which converts to kinetic energy when the arrow is released.
For a freely falling object, potential energy decreases as height reduces, while kinetic energy increases by an equal amount.
According to the law of conservation of energy, the total energy of an isolated system remains constant.
At the maximum height of a projectile thrown upwards, velocity is temporarily zero, making its kinetic energy zero.

Dimensions, Spring Constants, and Force Types

The spring constant (k = F / x) derived from Hooke's law (F = k × x) has the SI unit of N/m (Newton per meter).
Work done against gravity by a boy climbing stairs depends on mass, gravity, and height, but does not depend on time.
Watt-second is a unit of energy and is another name for Joule (E = P × t).
In atomic physics, the electron-volt (eV) measures energy, where 1 eV = 1.6 × 10⁻¹⁹ Joules.
Must knowThe work done by centripetal force on an object moving along a circular path is zero because force and displacement are perpendicular (θ = 90°).
Friction is a non-conservative force that always opposes motion (θ = 180°), resulting in negative work that dissipates as heat.
Gravitational force is a conservative force because the work done depends only on end points, not on the path taken.
The dimensional formula for power is [M L² T⁻³], derived from work divided by time.
The dimensional formula for work, kinetic energy, potential energy, and heat is [M L² T⁻²].

Mass-Energy Equivalence, Pendulums, and Work-Energy Theorem

Water stored behind a dam stores gravitational potential energy, which converts to kinetic energy as it falls.
Must knowEinstein's mass-energy equivalence equation is E = m × c², where c is the speed of light.
Power can also be expressed as P = F × v when force is constant and the object moves at a uniform velocity.
A machine doing 100 Joules of work in 10 seconds has a power of 10 Watts.
In a simple pendulum, kinetic energy is maximum and potential energy is zero at the mean position.
In a simple pendulum, potential energy is maximum and kinetic energy is zero at the extreme positions.
The work-energy theorem states that the net work done on an object equals the change in its kinetic energy (W = ΔK).
At escape velocity (11.2 km/s for Earth), the total mechanical energy of an object becomes zero.
Halving the mass and doubling the velocity doubles the overall kinetic energy.
Energy derived from food is measured in calories, where 1 Calorie = 4.184 Joules.
Burning coal transforms chemical energy into thermal/heat energy.

Key terms

Joule: SI unit of work and energy equal to one Newton-meter
Watt: SI unit of power equal to one Joule per second
Erg: CGS unit of work and energy equal to 10⁻⁷ Joules
Conservative Force: A force where total work done along a path is path-independent, such as gravity
Work-Energy Theorem: The theorem stating that net work done on a body equals the change in its kinetic energy

Formulas

W = F × d × cos(θ): Calculates work done by a force over a displacement at an angle θ
P = W / t: Calculates power as the rate of doing work over time
P = F × v: Calculates power delivered by a constant force at uniform velocity
K.E. = (1/2) × m × v²: Calculates the kinetic energy of an object with mass m and velocity v
P.E. = m × g × h: Calculates gravitational potential energy at height h
K.E. = p² / (2m): Relates kinetic energy to linear momentum p and mass m
E = m × c²: Einstein's equation for mass-energy equivalence

Quick revision

Read these the night before the exam.

Work is a scalar quantity with the SI unit of Joule.
1 horsepower is equal to 746 Watts.
1 kilowatt-hour equals 3.6 × 10⁶ Joules, representing 1 electric unit.
1 Joule equals 10⁷ Ergs, and 1 Newton equals 10⁵ Dynes.
Work done by a centripetal force moving along a circle is always zero.
Doubling the velocity of an object quadruples its kinetic energy.
Doubling the momentum of an object quadruples its kinetic energy.
The dimensional formula for work and energy is [M L² T⁻²].
The dimensional formula for power is [M L² T⁻³].
The earth's escape velocity is 11.2 km/s, at which total mechanical energy becomes zero.
1 electron-volt (eV) equals 1.6 × 10⁻¹⁹ Joules.
1 Calorie equals 4.184 Joules.

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