Work_ Energy And Power — Part 1 MCQs with Explanations

Work is done when a force causes an object to move a certain distance in the direction of the force. Let's look at the options: A) Force : Just having a force isn't enough. Think of pushing a heavy wall. You're applying force, but the wall doesn't move, so no work is done. B) Energy : Energy is the ability to do work. It's related to work, but not the same thing. You need energy to do work, but energy itself isn't work. C) Friction : Friction is a force that opposes motion. Friction can cause work to be done (e.g., rubbing your hands together creates heat, which is a form of energy). But friction isn't work itself. Work is done *by* or *against* the frictional force. D) Power : Power is the rate at which work is done. It tells you how quickly work is being done, not if work is being done at all. Therefore, work is only present if there is a force and the object moves in the direction of that force.

To calculate the work done by the man in pulling the trolley, we'll use the formula: Work (W) = Force (F) * Displacement (d) * cos(θ) Where: F = Force applied (50N) d = Displacement (30m) θ = Angle between the direction of force and the direction of displacement (assuming the force is applied in the direction of displacement, so cos(θ) = 1) Plugging the given values into the formula: W = 50N * 30m * 1 W = 1500J Therefore, the correct answer is Option A: 1500J .

Understanding the Question: This question is about work, energy, and power . It asks us to find the force needed to stop a moving car. What we know: * The car's initial speed is 72 km/h. We need to convert this to meters per second (m/s) because that's the standard unit for physics calculations. There are 1000 meters in a kilometer and 3600 seconds in an hour, so 72 km/h = (72 * 1000) / 3600 = 20 m/s. * The car stops in 4 seconds (this is the time it takes for the car to decelerate to 0 m/s). * The car's mass is 1000 kg. What we need to find: We need to calculate the force applied by the brakes to bring the car to a complete stop. How to solve it: First, we need to find the deceleration (or negative acceleration) of the car. Deceleration is the change in speed divided by the time it takes for that change to occur. The change in speed is from 20 m/s to 0 m/s, and the time is 4 seconds. Deceleration = (final speed - initial speed) / time = (0 - 20 m/s) / 4 s = -5 m/s² (The negative sign indicates deceleration). Next, we use Newton's second law of motion : Force = mass × acceleration. In this case, the acceleration is actually a deceleration, so we use the negative value. Force = 1000 kg × (-5 m/s²) = -5000 N The magnitude of the force (ignoring the negative sign, which just tells us the direction) is 5000 N, which is the same as 5.0 × 10³ N. Therefore, the correct answer is D: 5.0 × 10³ N

To find the height, we use the formula for gravitational potential energy: Potential Energy (PE) = m × g × h Where: PE = 9800 J (Energy used) m = 70 kg (Mass of the object) g = 10 m/s² (Acceleration due to gravity, commonly used in numerical problems) h = ? (Height) Substituting the given values: 9800 = 70 × 10 × h 9800 = 700h h = 9800 ÷ 700 = 14 m Therefore, the 70 kg object was lifted to a height of 14 metres . Note: Options with negative height are incorrect because the object is being lifted upward , so the height must be positive.

The correct answer is A: Mechanical. Mechanical energy is the energy an object has due to its motion or position. It's actually the sum of two types of energy : Kinetic energy: This is the energy of motion. Any moving object has kinetic energy (like a rolling ball). Potential energy: This is stored energy based on an object's position or condition. For example, a ball held high above the ground has gravitational potential energy. Electric energy is associated with the flow of electrons and electric charges. Chemical energy is stored in the bonds of atoms and molecules. It's released during chemical reactions (like burning wood). Sound energy is energy that travels as waves through a medium (like air or water). Therefore, only mechanical energy is defined as having two distinct types (kinetic and potential).

Work is defined in physics as the product of force and displacement in the direction of the force . This means that work is only said to be done when a force causes displacement of a body . If there is no displacement, even if a force is applied, no work is done in the physics sense. Option A is incorrect because energy gain alone doesn't confirm that mechanical work has occurred—it must involve displacement. Option B is misleading; forces may act on a body, but without displacement, no work is done. Option D is close, but too vague—movement alone isn't enough; it must be displacement caused by a force . Therefore, Option C is correct because displacement is the essential condition for work to be done on a body.

Weight is the gravitational force acting on an object and is related to mass by the formula: Weight (W) = Mass (m) × Acceleration due to gravity (g) Where: W = 450 N (Weight of the girl) g = 9.8 m/s² (Standard acceleration due to gravity) m = ? (Mass of the girl) Rearranging the formula: Mass (m) = Weight (W) ÷ g Substituting the given values: m = 450 ÷ 9.8 ≈ 45.9 kg Therefore, the mass of the girl is approximately 45.9 kg . Remember: Mass is measured in kilograms (kg) and remains the same everywhere, whereas weight is measured in newtons (N) and depends on the value of gravitational acceleration. Therefore, a person can have the same mass but different weights on different planets.

Let's understand potential energy first. Potential energy (PE) is the energy an object has because of its position or height. The formula for potential energy is: PE = mgh , where: m is the mass of the object, g is the acceleration due to gravity (which is constant), and h is the height of the object. Notice that the velocity of the object doesn't appear in the formula for potential energy. Potential energy depends only on the mass, gravity, and height. Changing the velocity of the object at a certain height does not change its height . Since the height remains the same, and the mass and gravity are also constant, the potential energy will not change . Therefore, the correct answer is A: Potential energy will be constant.

The work done by the stopping force in bringing a body to rest is equal to its initial kinetic energy . Work done = Force × Distance = Kinetic Energy If the same retarding force is applied to the truck, car, and motorcycle, and all three have the same kinetic energy , then: Distance travelled before stopping = KE / Force Since KE is equal for all and Force is also equal, the stopping distance will be the same for each vehicle. Therefore: X = Y = Z Hence, the correct option is E .

The correct answer is Option C: Electrical energy Here's why: * Stored energy means energy that is held within an object or system and can be released later. * Nuclear energy: This is energy stored within the nucleus of an atom. Think of nuclear power plants. * Potential energy: This is energy an object has because of its position or condition. A stretched rubber band or a book on a high shelf has potential energy. * Chemical energy: This is energy stored in the bonds of molecules. Think of the energy in food or gasoline. * Electrical energy: While we use electricity to *transfer* energy, it is generally considered as a form of kinetic energy (the energy of moving electric charges), not a form of *stored* energy. It is the flow of electrons. Therefore, electrical energy is not typically classified as stored energy in the same way as the other options.

When the car is at rest, the total weight of the car is evenly distributed among the four wheels. So, each wheel experiences a reaction force of R. When the car is moving, the engine provides a forward force . Due to inertia, there is a tendency for the car's weight to shift towards the rear wheels . Think about when you accelerate in a car; you feel pushed back into your seat. This weight shift means that the rear wheels will bear a slightly larger portion of the car's weight . Consequently, the front wheels will bear a slightly smaller portion of the car's weight. Therefore, the reaction force at either of the front wheels will be less than R . The correct answer is Option B.

A bullet fired by the gun is the correct answer to “Which of the following can do more work”. This question is standard in competitive examination syllabi for Work_ Energy And Power.

The sum of the kinetic energy and potential energy of an object is the correct answer to “Mechanical energy is”. This question is standard in competitive examination syllabi for Work_ Energy And Power.

Potential energy is the correct answer to “A compressed spring possesses more energy than a spring of normal length because the compressed spring has-”. This question is standard in competitive examination syllabi for Work_ Energy And Power.

Density is the correct answer to “Mass/Volume =”. This question is standard in competitive examination syllabi for Work_ Energy And Power.

α-particle is the correct answer to “The following particles move with same kinetic energy. Which of them has maximum momentum”. This question is standard in competitive examination syllabi for Work_ Energy And Power.

force is the correct answer to “An object moves at a constant speed when no acting on it.”. This question is standard in competitive examination syllabi for Work_ Energy And Power.

Kinetic energy is the correct answer to “At the time of releasing an arrow in a drawn bow, the potential energy of the bow change”. This question is standard in competitive examination syllabi for Work_ Energy And Power.

force is the correct answer to “Which of the following physical units changes or tends to change the state of rest or uniform motion of an object”. This question is standard in competitive examination syllabi for Work_ Energy And Power.

646.8J is the correct answer to “When an object of 11 kg is at a height of 6 m from the ground, then find the energy contained in it? (g = 9.8ms -2 )”. This question is standard in competitive examination syllabi for Work_ Energy And Power.

3.6 × 106 J is the correct answer to “Which one of the following is the value of 1 kwh of energy converted into joules”. This question is standard in competitive examination syllabi for Work_ Energy And Power.

motor is the correct answer to “The conversion of mechanical energy into electrical energy does not occur in”. This question is standard in competitive examination syllabi for Work_ Energy And Power.

-2.25 ms-1 is the correct answer to “A 30 gram bullet is fired horizontally with a velocity of 150 ms -1 from a 2 kg pistol. What is the expected velocity of the pistol”. This question is standard in competitive examination syllabi for Work_ Energy And Power.

U = mgh is the correct answer to “Formula for gravitational potential energy is-”. This question is standard in competitive examination syllabi for Work_ Energy And Power.

100J is the correct answer to “The kinetic energy of an object of mass m moving at a speed of 5 ms -1 is 25J. What will be its kinetic energy when its speed will be double”. This question is standard in competitive examination syllabi for Work_ Energy And Power.

mass and velocity is the correct answer to “Product of momentum expressed as”. This question is standard in competitive examination syllabi for Work_ Energy And Power.

external force, rigidity is the correct answer to “Despite . . . . . . . . working on a substance, the quality to not change in shape is called . . . . . . . .”. This question is standard in competitive examination syllabi for Work_ Energy And Power.

Kinetic energy + potential energy is the correct answer to “What does mechanical energy equal”. This question is standard in competitive examination syllabi for Work_ Energy And Power.

The same amount of work with lesser force is the correct answer to “A simple machine helps a person in doing”. This question is standard in competitive examination syllabi for Work_ Energy And Power.

Only kinetic is the correct answer to “The energy of wind is”. This question is standard in competitive examination syllabi for Work_ Energy And Power.

Work/Time is the correct answer to “What is the formula for power-”. This question is standard in competitive examination syllabi for Work_ Energy And Power.

275J is the correct answer to “What will be the kinetic energy of an object weighing 22 kg moving at a speed of 5 m/s”. This question is standard in competitive examination syllabi for Work_ Energy And Power.

Potential energy is the correct answer to “What does the raised hammer have”. This question is standard in competitive examination syllabi for Work_ Energy And Power.

Initial velocity of object is the correct answer to “Which of the following the work done by a body does not depend on”. This question is standard in competitive examination syllabi for Work_ Energy And Power.

Raised hammer is the correct answer to “Which of the following does not have kinetic energy”. This question is standard in competitive examination syllabi for Work_ Energy And Power.

Is zero is the correct answer to “If an object is rotated in a circular path, what will be the work done on it in one rotation”. This question is standard in competitive examination syllabi for Work_ Energy And Power.

Total used energy/total time is the correct answer to “The average power is equal to which of the following”. This question is standard in competitive examination syllabi for Work_ Energy And Power.

500J is the correct answer to “A force of 50 N displaces an object 10 m. What will be the work done by the force”. This question is standard in competitive examination syllabi for Work_ Energy And Power.

in the opposite direction is the correct answer to “Body A whose mass is 2 kg and body B whose mass is 3 kg are moving towards each other at a velocity of 4 m/s and 2 m/s respectively, at the time of collision the elastic impact will be-”. This question is standard in competitive examination syllabi for Work_ Energy And Power.

$$\frac{W}{t}$$ is the correct answer to “If an agent doing 'W' works in time 't', then his power will be-”. This question is standard in competitive examination syllabi for Work_ Energy And Power.