Work , energy and power
Science

In this article, we will study about theory of Work, Energy and Power With MCQs.

 

Work

The work done by a force is defined to be the product of the component of the force in the direction of the displacement and the magnitude of this displacement.

Work Done is Dot product of Force and displacement = (mod of F)*(mod of D)*cosθ

Where W is the work done, F is the force, d is the displacement, θ is the angle between force and displacement and F cosθ is the component of force in the direction of displacement.

Displacement * :- It is the shortest distance between any two points , it is a vector quantity i.e. it has direction also .

We understand from the work equation that if there is no displacement, there is no work done, irrespective of how large the force is. To summarize, we can say that no work is done if:

  • the displacement is zero
  • the force is zero
  • the force and displacement are mutually perpendicular to each other.

The SI unit of work is Joule (J).

 

Energy

Energy is the ability to do work. It’s what enables us to move, grow, and basically do anything in life. Think of energy as fuel in a car. Just like the car needs fuel to move, we need energy to do work.

The unit of Energy is the same as of Work, i.e. Joules. Energy is found in many things, and thus there are different types of energy.

There are two main types of energy:

  • Kinetic Energy: The energy of motion. When something is moving, it has kinetic energy.
  • Potential Energy: The energy stored in an object. For example, when you stretch a rubber band, it has the potential to snap back. That’s potential energy.

Some other types of energy are given below:

  • Mechanical energy
  • Mechanical wave energy
  • Chemical energy
  • Electric energy
  • Magnetic energy
  • Radiant energy
  • Nuclear energy
  • Ionization energy
  • Elastic energy
  • Gravitational energy
  • Thermal energy
  • Heat Energy

Power

 

Power is the rate at which work is done or energy is used. If you think about two people pushing the same shopping cart, one person might be stronger and can push it faster. This person is using more power because they are doing the same work in less time.

Formula:

Power=Work / Time

The SI unit of power is Watt (W).

 

Work and Energy: A Connection

 

Work and energy are closely related because work is a way to transfer energy. When you do work on an object, you’re essentially giving it energy or taking energy away. Let’s explore this :

  • Doing Work to Give Energy:
  •    When you apply force to an object and move it over a distance, you’re doing work on it. This work gives the object kinetic energy, or energy of motion. For example, pushing a sled down a hill gives it the energy to slide.
  • Doing Work to Take Energy Away:
  •     On the other hand, if you apply force in the opposite direction to the movement, like when you’re pulling a sled uphill, you’re doing work that takes away its kinetic energy, converting it back to potential energy.
  • Work-Energy Principle: This is a key concept that states that the work done on an object is equal to the change in its kinetic energy. If you do positive work on something (like pushing it), you increase its kinetic energy. If you do negative work (like applying brakes to a moving car), you decrease its kinetic energy. Certainly! Here’s a brief explanation of the theory on work, energy, and power, followed by some multiple-choice questions (MCQs) to test your understanding.

Formula:

Work Done=Change in Kinetic Energy={m(v²−u²)}/2

Here:

  • m is the mass of the object
  • v is the final velocity
  • u is the initial velocity

MCQs on Work , Energy and Power :-

Question 1: What is Work?
  1. A) The amount of energy consumed
  2. B) Force multiplied by distance in the direction of force
  3. C) Force divided by distance
  4. D) Mass multiplied by acceleration

Answer: B)

 

Question 2: What type of energy is stored in a stretched rubber band?
  1. A) Kinetic Energy
  2. B) Thermal Energy
  3. C) Potential Energy
  4. D) Electric Energy

Answer: C)

Question 3: If the velocity of an object is doubled, what happens to its kinetic energy?
  1. A) Remains the same
  2. B) Halves
  3. C) Doubles
  4. D) Quadruples

Answer: D)

Question 4: What is Power in terms of Work and Time?
  1. A) Power = Work + Time
  2. B) Power = Work × Time
  3. C) Power = Work / Time
  4. D) Power = Time / Work

Answer: C)

Question 5: If no distance is covered by the force applied, what is the work done?
  1. A) Equal to the force
  2. B) Half of the force
  3. C) Zero
  4. D) Double the force

Answer: C) Zero

Question 6: What form of energy is possessed by a moving car?
  1. A) Potential Energy
  2. B) Chemical Energy
  3. C) Electrical Energy
  4. D) Kinetic Energy

Answer: D) Kinetic Energy

 

Question 7: What happens to the gravitational potential energy of an object as it is raised higher above the ground?
  1. A) Increases
  2. B) Decreases
  3. C) Remains the same
  4. D) Becomes negative

Answer: A) Increases.

Question 8: If the work done on an object is negative, what can you conclude?
  1. A) The object is moving faster
  2. B) The object’s kinetic energy is increasing
  3. C) The object’s kinetic energy is decreasing
  4. D) The object is at rest

Answer: C) The object’s kinetic energy is decreasing

 

Question 9: What is the unit of power in the International System of Units (SI)?
  1. A) Joule
  2. B) Watt
  3. C) Newton
  4. D) Meter

Answer: B) Watt

 

Question 10: Which of the following is NOT a form of energy?
  1. A) Thermal Energy
  2. B) Chemical Energy
  3. C) Force
  4. D) Electrical Energy

Answer: C) Force

 

Question 11: In a frictionless system, what is the relationship between total kinetic and potential energy?
  1. A) Always Increasing
  2. B) Always Decreasing
  3. C) Always Equal
  4. D) Constant (Conservation of Mechanical Energy)

Answer: D)

Question 12: A motor does 5,000 Joules of work in 10 seconds. What is its power output?
  1. A) 500 Watts
  2. B) 50 Watts
  3. C) 5000 Watts
  4. D) 50,000 Watts

Answer: A)

 

Question 13: A moving object has which type of energy?
  1. A) Potential Energy
  2. B) Chemical Energy
  3. C) Kinetic Energy D

) Heat Energy

Answer: C) Kinetic Energy

 

Question 14: If the mass of an object is doubled while keeping the velocity constant, what happens to its kinetic energy?
  1. A) Remains the same
  2. B) Doubles
  3. C) Halves
  4. D) Quadruples

Answer: B) Doubles

 

Question 15: What is the work done on an object moving in a circle at a constant speed?
  1. A) Zero
  2. B) Increasing
  3. C) Decreasing
  4. D) Constant

Answer: A) Zero

 

Question 16: If you lift an object up, then the work done by gravity is:
  1. A) Positive
  2. B) Negative
  3. C) Zero
  4. D) Infinite

Answer: B) Negative

 

Question 17: Which of the following is true for a system where only conservative forces are acting?
  1. A) Kinetic energy is constant
  2. B) Potential energy is constant
  3. C) Mechanical energy is constant
  4. D) No energy is conserved

Answer: C) Mechanical energy is constant

 

Question 18: What does 1 Watt equal in terms of Joules and seconds?
  1. A) 1 Joule per second
  2. B) 1 Joule per minute
  3. C) 1 Joule per hour
  4. D) 10 Joules per second

Answer: A) 1 Joule per second

 

Question 19: An object is at its maximum potential energy when:
  1. A) It’s at the lowest point
  2. B) It’s at the highest point
  3. C) It’s in motion
  4. D) It’s at rest

Answer: B) It’s at the highest point

 

Question 20: If two objects have the same momentum, they must have the same:
  1. A) Mass
  2. B) Velocity
  3. C) Kinetic Energy
  4. D) None of the above

Answer: D) None of the above

These questions delve deeper into the fascinating interplay between work, energy, and power. Understanding these concepts is essential, not only for those studying physics but also for everyday applications, as they describe the fundamental mechanics of how our world operates.

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