Work, Energy and Power Practice Questions
20 free Work, Energy and Power practice questions for the General Science. Tap an option to answer — you get instant feedback, the correct answer, and a detailed explanation for every question.
Which of the following conditions must be met for work to be done on an object in the scientific sense?
- A A force must be applied, regardless of whether any movement occurs.
- B An object must move in any direction regardless of the applied force.
- C A force must be applied, and the object must move in the force's direction.
- D The object must remain stationary while a sufficiently large force is applied.
Correct answer: A force must be applied, and the object must move in the force's direction.
Work is defined as the product of the component of the force in the direction of the displacement and the magnitude of this displacement. If there is no displacement, or if the force is perpendicular to the displacement, the work done is zero.
What is the SI unit of Work and Energy?
- A Watt
- B Newton
- C Joule
- D Pascal
Correct answer: Joule
The Joule (J) is the standard unit for both work and energy. One Joule is defined as the work done by a force of one Newton acting through a distance of one meter.
If the velocity of a moving object is doubled, what happens to its kinetic energy?
- A It is doubled.
- B It remains the same.
- C It is quadrupled.
- D It is halved.
Correct answer: It is quadrupled.
Kinetic energy is calculated using the formula $KE = \frac{1}{2}mv^2$. Since the velocity ($v$) is squared, doubling the velocity results in $2^2$ or a four-fold increase in energy.
A person holds a heavy suitcase and waits for a bus for 15 minutes. How much work is done by the person on the suitcase during this time?
- A Zero work done
- B Positive work
- C Negative work
- D Depends on the suitcase weight
Correct answer: Zero work done
Work is done only when a force causes a displacement. Since the suitcase remains stationary despite the force applied to hold it up, the displacement is zero, resulting in zero work done.
Which type of energy is possessed by a stretched rubber band or a compressed spring?
- A Kinetic Energy
- B Chemical Energy
- C Elastic Potential Energy
- D Gravitational Potential Energy
Correct answer: Elastic Potential Energy
Elastic potential energy is stored in objects that are compressed, stretched, or otherwise deformed. Once the force is released, this stored energy can perform work, such as launching a projectile.
Power is defined as the:
- A Ability to do work.
- B Rate of doing work.
- C Total energy consumed.
- D Force applied per unit area.
Correct answer: Rate of doing work.
Power is the measure of how fast work is being done or how fast energy is being transferred. It is calculated by dividing the work done by the time taken ($P = W/t$).
One Horsepower (hp) is approximately equal to how many Watts?
- A 500 W
- B 746 W
- C 1000 W
- D 1200 W
Correct answer: 746 W
The horsepower is a non-SI unit of power traditionally used in the automotive and engineering industries. One standard mechanical horsepower is equivalent to 746 Watts.
The Law of Conservation of Energy states that:
- A Energy can be created from nothing.
- B Energy can be destroyed during a collision.
- C Energy can only be transformed from one form to another.
- D Total energy in a system always decreases over time.
Correct answer: Energy can only be transformed from one form to another.
This fundamental principle of physics states that the total energy of an isolated system remains constant. Energy may change form—such as from potential to kinetic—but the sum total never changes.
A 10 kg object is lifted to a height of 5 meters. Taking $g = 10 m/s^2$, what is its gravitational potential energy?
- A 50 J
- B 100 J
- C 500 J
- D 15 J
Correct answer: 500 J
Gravitational potential energy is calculated as $PE = mgh$. For this object, $10 kg \times 10 m/s^2 \times 5 m = 500 J$.
Which of the following is a unit of commercial electrical energy consumption?
- A Kilowatt
- B Kilowatt-hour
- C Joule per second
- D Volt-Ampere
Correct answer: Kilowatt-hour
The kilowatt-hour (kWh) is a unit of energy, not power. It represents the energy consumed by a 1000-watt appliance running for one hour.
When an object falls freely towards the ground, its total mechanical energy:
- A Increases
- B Decreases
- C Remains constant
- D Becomes zero
Correct answer: Remains constant
In the absence of air resistance, the loss in potential energy is exactly equal to the gain in kinetic energy. Thus, the sum of $PE + KE$ (total mechanical energy) remains the same throughout the fall.
What happens to the work done if the force and displacement are in opposite directions (angle is 180 degrees)?
- A Work is positive.
- B Work is negative.
- C Work is zero.
- D Work is infinite.
Correct answer: Work is negative.
When the force opposes the motion (like friction), the work done is negative. Mathematically, $W = Fd \cos(180^{\circ})$, and since $\cos(180^{\circ}) = -1$, the value is negative.
A machine does 2000 Joules of work in 20 seconds. What is the power of the machine?
- A 100 W
- B 4000 W
- C 40,000 W
- D 10 W
Correct answer: 100 W
Using the formula $P = W/t$, we get $2000 J / 20 s = 100 Watts$.
Which of the following energy transformations occurs in a battery-operated flashlight?
- A Electrical to Chemical to Light
- B Chemical to Electrical to Light
- C Light to Chemical to Electrical
- D Kinetic to Electrical to Light
Correct answer: Chemical to Electrical to Light
The battery stores chemical energy, which is converted into electrical energy when the circuit is closed, which is then converted into light (and heat) energy by the bulb.
If a force is applied to an object but the object moves perpendicular to the direction of the force, the work done is:
- A Maximum
- B Minimum but not zero
- C Zero
- D Negative
Correct answer: Zero
Work is $W = Fd \cos(\theta)$. When the angle $\theta$ is $90^{\circ}$, $\cos(90^{\circ}) = 0$, meaning no work is done by that specific force (e.g., centripetal force in circular motion).
The energy of a body due to its motion is called:
- A Potential energy
- B Kinetic energy
- C Thermal energy
- D Nuclear energy
Correct answer: Kinetic energy
Kinetic energy is the energy that a body possesses by virtue of being in motion. It depends on both the mass of the object and the square of its speed.
Which of the following is NOT a scalar quantity?
- A Work
- B Energy
- C Power
- D Force
Correct answer: Force
Work, energy, and power are all scalar quantities, meaning they have magnitude but no direction. Force is a vector quantity because it has both magnitude and direction.
In a hydroelectric power plant, what is the primary energy transformation?
- A Nuclear energy to electrical energy
- B Potential energy of water to electrical energy
- C Chemical energy to kinetic energy
- D Solar energy to potential energy
Correct answer: Potential energy of water to electrical energy
Water stored at a height has potential energy. As it falls, it turns into kinetic energy which rotates turbines, finally being converted into electrical energy.
How many Joules are in one kilowatt-hour (kWh)?
- A 1,000 J
- B 36,000 J
- C 3.6 x 10^6 J
- D 3.6 x 10^5 J
Correct answer: 3.6 x 10^6 J
$1 kWh = 1000 W \times 3600 s = 3,600,000 Joules$. This can be written in scientific notation as $3.6 \times 10^6 J$.
An object's mechanical energy is the sum of its:
- A Heat and light energy
- B Kinetic and potential energy
- C Mass and velocity
- D Chemical and nuclear energy
Correct answer: Kinetic and potential energy
Mechanical energy is the energy associated with the motion and position of an object. It is the total of its kinetic energy (motion) and its potential energy (position or stored state).