Work Energy and Power MCQs

 

Work is something that is accomplished by the action of a force. The measure of transfer of energy occurs when an object is moved by a distance due to an external force applied in the direction of the displacement. If we apply a constant force, then the work can be calculated by multiplying the distance covered by the component and the force which is acting along the path. To express this mathematically, work done W is equal to the force exerted f times the distance covered d, or 

W = fd. 

The time rate at which the work is being done or energy is delivered is called power, which can be expressed as the amount of work done W, or energy transferred, against the time interval t or W/t. The Units of power can be expressed as work (or energy) per unit time, foot-pounds per minute, joules per second (or watts), and ergs per second. Power can also be expressed as the product of the force applied to move an object and the speed of the object in the direction of the force.

The capacity for doing work that exists in potential, kinetic, thermal, electrical, chemical, nuclear, or other various forms is called energy. Energy can neither be created nor be destroyed but it can be transferred from one form to the other like heat energy can be converted into light energy, chemical energy can be converted into heat energy etc.

MCQs based of Work, Energy & Power

Ques 1. The energy held by an object due to its motion is

1. Motion Energy
2. Kinetic Energy
3. Potential Energy
4. Total Energy

Answer: (b) Kinetic Energy

Explanation: The energy an object possesses due to its motion is called Kinetic Energy. In order to accelerate an object, we must apply a force that requires us to do work. The energy is being transferred to the object after the work has been done and so the object would be moving with a new constant speed.

Ques 2. Kinetic Energy is

1. Scalar
2. Vector
3. Tensor
4. None of these

Answer: (b) Scalar

Explanation: Kinetic energy is a scalar quantity not a vector as it does not have a direction. unlike velocity, acceleration, force. So a cricket ball thrown to the right with a velocity of 10 m/s, has the exact same kinetic energy as a cricket ball thrown down with a velocity of 10 m/s.

Ques 3. In a demonstration, a sharp-shooter fires a bullet of mass 50.0 g with speed 200 m s-1 on soft plywood of thickness 2.00 cm. The bullet comes through the wood with only 10% of its initial kinetic energy. What is the speed of the bullet when it comes out of the plywood?

1. 61 ms-1
2. 100 ms-1
3. 63.2 ms-1
4. 65.7 ms-1

Answer: (c) 63.2 ms-1

Explanation: The initial kinetic energy of the bullet is mv2/2 = 1000 J. The Final kinetic energy of the bullet is 0.1×1000 = 100 J. If vf is the speed in which the bullet emerges, 

12m vf2 = 100 J

Vf = 2 100 J0.05 kg

vf= 63.2 ms-1

Ques 4. How fast would a 1 kg bowling ball travel if it had the same kinetic energy as that of the elephant provided the mass of the elephant is 6000 kg and velocity given is 10 m/s?

1. 1000 m/s
2. 775 m/s
3. 625 m/s
4. 820 m/s

Answer: (b) 775 m/s

Explanation: Kbowling ball = Kelephant

12 mbowling ball.v2 =12 melephant.v2

vbowling ball= mass of elephant.v2 mass of ball = 775 m/s

Ques 5. The energy possessed by a body due its position is 

1. Kinetic Energy
2. Potential Energy
3. Total Energy
4. Position Energy

Answer: (b) Potential Energy

Explanation: The energy that is possessed by a body due to its position relative to other objects is called potential energy which stresses within itself, its electric charge, or other factors.

 

Ques 6. Scalar Product is

1. A.B = AB sin x
2. A x B = AB sin x
3. A.B = AB cos x
4. A x B = AB cos x

Answer: (c) A.B= AB cos x

Explanation: The scalar or dot product of two vectors A and B is written as A.B and is a scalar quantity given by : A.B = AB cos θ, where θ is the angle between A and B. It can be positive, negative or zero depending upon the value of θ.

Ques 7. Scalar Product is

1. Commutative
2. Not Commutative
3. Both Commutative and Non-Commutative
4. None of these

Answer: (c) Commutative

Explanation: The scalar product is commutative. This means a.b = b.a

Ques 8. Scalar product obeys the distributive law which means 

1. A.(B+C)=A.B+A.C
2. Ax(B+C)=AxB+AxC
3. Both a and b
4. None of these

Answer: (a) A.(B+C)=A.B+A.C

Explanation: Scalar product obeys the distributive law:

1. (B + C) = A.B + A.C

Further, λ A. (λ B) = λ (A.B)

where λ is a real number.

Ques 9. Work is expressed as:

1. W= F.d
2. W= F x d
3. W= FD
4. None of these

Answer: (a) W=F.d

Explanation: Work can be expressed as the product of force and displacement. It is the application of force along with displacement.

Ques 10. Potential and Kinetic energy are:

1. Mechanical energy
2. Electrical energy
3. Magnetic energy
4. None of these

Answer: (a) Mechanical Energy

Explanation: Mechanical Energy is the sum of the kinetic energy (energy of motion), and the potential energy, (energy stored in a system by reason of the position of its parts.)

Ques 11. Power is expressed as

1. P = dW/dt
2. P = F * d
3. P = E
4. P = dE/dt

Answer: (a) P = dW/dt

Explanation: The rate of change of work is called power. Hence, 

P = dW/dt. 

Instantaneous power = Force x instantaneous speed. 

Average power = total work / total time.

Ques 12. Energy involved in creating work _____

1. Gets used up
2. Gets transferred
3. Gets exhausted
4. Gets lost

Answer: (b) Gets transferred

Explanation: Energy engaged with making work gets moved or changed over into another form of energy. Energy can neither be created nor be destroyed. Thus, the energy included will get changed over into another type of energy. Generally in mechanical work, the energy gets scattered as heat energy.

Ques 13. An object with weight of 100 N is kept at a height of 15m. Find the Potential Energy of the object at that height. 

1. 1500 J
2. 1510 J
3. 1520 J
4. 1530 J

Answer: Potential Energy is given by, PE=mgH

Given mg=100N and H=15 m

PE=100×15=1500 J

Ques 14. The work done by a body is 50 kJ, which it attains while reaching a height of 5 m. By what difference has the energy of the body changed?

1. 50 kJ
2. -50 kJ
3. 25 kJ
4. 10 kJ

Answer: (a) 50 kJ

Explanation: According to the work-energy theorem, the entire change in kinetic energy is equal to the entire work done. Therefore, the entire change in energy is 50 kJ. Since only the ‘amount’ has been asked, the sign, which denotes the direction of energy transfer, doesn't matter.

Ques 15. A cricket ball having 7 kg of mass which is moving with a velocity of 20 m/s covers a height of 8.75 m vertically. Calculate the work done in J? Assume g = 10 m/s².

1. 0
2. 10
3. 15
4. 20

Answer: (a) 0

Explanation: According to the work-energy theorem, the total work done on a body is equal to the change in the total energy. 

K.E. = 12mv²

P.E. = mgH. By using these, we can find out the net change in the kinetic and potential energies at the starting and after covering a distance of 8.75 m. Since, the total change in energy is 0, the work done is 0.

Ques 16. Work done is the scalar product of

1. Force and displacement vectors
2. Force and distance
3. All of these
4. None of these

Answer: (a) Force and displacement vectors

Explanation: Work done is a scalar product of force and displacement, which are both vectors.

 Part @2

1. The rate of doing work is called ——————-

1. Force
2. Acceleration
3. Power
4. Displacement

Answer: (c) Power

Explanation: Power is defined as the rate of doing work.

2. Which is the type of collision in which both the linear momentum and the kinetic energy of the system remain conserved?

1. Inelastic Collision
2. Elastic Collision
3. Destructive collision
4. None of the options

Answer: (b) Elastic Collision

Explanation: In an elastic collision, the linear momentum and the kinetic energy of the system remain conserved.

3. Collision between marble balls is which type of collision?

1. Inelastic Collision
2. Elastic Collision
3. Destructive collision
4. None of the options

Answer: (b) Elastic Collision

Explanation: Collision between marble balls is an example of elastic collision.

4. The energy possessed by the body by virtue of its motion is known as?

1. Chemical energy
2. Thermal energy
3. Potential energy
4. Kinetic energy

Answer: (d) Kinetic energy

Explanation: The energy possessed by a body by virtue of its motion is known as its kinetic energy. It is given by the formula,

$\begin{array}{l}��=\frac{1}{2}�{�}^2\end{array}$

5. Find the potential energy stored in a ball of mass 5 kg placed at a height of 3 m above the ground.

1. 121.20 J
2. 147.15 J
3. 227.31 J
4. 182.21 J

Answer: (b) 147.15 J

Explanation: m = 5 kg, h = 3 m, g = 9.81 m/s-2

We know that, Potential energy = mgh

= 5 * 9.81 * 3 = 147.15 J

6. What is the power utilised when work of 1000 J is done in 2 seconds?

1. 100 W
2. 200 W
3. 20 W
4. 500 W

Answer: (d) 500 W

Explanation: W=1000J, t=2 seconds

Power=work/time = 1000/2 = 500 W

7. State true or false: According to Equivalence of Mass and Energy, it states that mass and energy are NOT interconvertible.

1. True
2. False

Answer: (b) False

Explanation: According to Equivalence of Mass and Energy put forth by Einstein, it states that mass and energy are interconvertible.

$\begin{array}{l}�=�{�}^2\end{array}$

8. Which one has higher kinetic energy? Both light and heavy bodies have equal momenta.

1. Heavy body
2. Light body
3. Both
4. None of the options

Answer: (b) Light body

Explanation: Since, the momenta of the heavy body and light body are same, thus the velocity of light body is greater than that of heavy body. Also, kinetic energy is proportional to the square of velocity. Hence, the lighter body has greater kinetic energy.

9. An electric heater of rating 1000 W is used for 5 hrs per day for 20 days. What is the electrical energy utilized?

1. 100 kWh
2. 200 kWh
3. 120 kWh
4. 500 kWh

Answer: (a) 100 kWh

Explanation: The power of the electric heater is 1000 W, and the time period is 20×5 = 100 hr.

Electrical energy = Power × Time

Electrical energy = 1000 × 100 = 100000 Wh

Electrical energy = 100 kWh

10. A ball moves in a frictionless inclined table without slipping. The work done by the table surface on the ball is

1. Negative
2. Zero
3. Positive
4. None of the options

Answer: (b) Zero

Explanation: The work done by a ball when it moves on a frictionless inclined table without slipping is zero.