Work Power And Energy(12th Grade > Physics ) Questions and answers for exam Preparation

12th Grade > Physics

WORK POWER AND ENERGY MCQs

Work And Energy, Sources Of Energy, Electric Potential Energy Potential And Dipoles

Total Questions : 109 | Page 3 of 11 pages

Question 21. How is sunlight responsible for wind energy?

Differential heating of different landforms causes pressure difference.
Sunlight converts kinetic energy of air molecules to chemical energy.
Sunlight decreases friction in air and thus facilitates air movement.
Radiation coming from sun drags the air along itself.

Discuss Question

Answer: Option A. -> Differential heating of different landforms causes pressure difference.
:
A
Different parts of Earth receive different intensity of sunlight and also different landforms have different ability to heat-up. The air mass above hotter regions develop low pressure and that above colder regions develop high pressure. Wind blows from high pressure region to low pressure region. Thus sunlight is the ultimate source of energy for winds.

Question 22. Which of the following resources is exhaustible?

Fossil fuels
Wind energy
Hydro energy
Nuclear energy

Discuss Question

Answer: Option A. -> Fossil fuels
:
A
The exhaustible natural resources are limited in nature and can be exhausted by different human activities. The inexhaustible natural resources are in unlimited quantity and are not likely to be exhausted by human activities. Fossil fuels are exhaustibleresources, whereas hydro energy, nuclear energy, and wind energy areinexhaustible natural resources.

Question 23. Which of the following statement is true regarding the hydropower plant?

The potential energy possessed by the stored water is converted into electricity.
Kinetic energy possessed by the stored water is converted into potential energy.
Electricity is extracted from the chemical energy possessed by water.
Water is converted into steam to produce electricity.

Discuss Question

Answer: Option A. -> The potential energy possessed by the stored water is converted into electricity.
:
A
Waterstored in a dam at a certain height,haspotential energy. This potential energy isconverted to kinetic energy when allowed to flow. The kinetic energy of flowing water is used to turn the turbine, which is used to generate electric current. Hence, the overall conversion is from the potential energy of stored water to electrical energy.

Question 24. A boy tied a string to one of the ends of a box and started sliding the box on a playground. He then observed a circular track and rushed there and completed half revolution of the track with his box. The work done by friction on the box is _____.

negative
zero
positive
infinite

Discuss Question

Answer: Option A. -> negative
:
A

A Boy Tied A String To One Of The Ends Of A Box And Started ...

When box slides on the ground, friction will act on the boxopposite to the direction of motion. Even on the circular track, if we take any small portion, friction is always opposite to the displacement. Hence work done by the friction =- force

\times

displacement. Therefore, thework done by friction on the toy isnegative work.

Question 25. The mechanical energy in a system remains constant.

True
False
7 m
9 m

Discuss Question

Answer: Option A. -> True
:
A
Mechanical energy is the sum of kinetic energy and potential energy in a system.
The law of conservation of mechanical energy states that the mechanical energy in a systemremains constant as long as the forces applied are conservative(doesn't depend on the path).

Question 26. A loader applied

150 N

of force to lift a stone and

1250 J

of work was done by it. How far was the rock lifted during the application of force?

9.3 m
10.3 m
8.3 m
7.3 m

Discuss Question

Answer: Option C. -> 8.3 m
:
C
Given:
Work done,

W = 1250 J

Force,

F = 150 N

Let the distance the rock was raised be

s

.
Work done is the product of force and displacement of the body along the force.

W = F s

s = \frac{1250}{150} = 8. ¯ 3 m

Thus, the rock was lifted through a distance of

8.3 m

Question 27. An electron and a proton are at a distance of

1 ˙ A

. The dipole moment will be

(C \times m)

1.6×1019
1.6×10−29
3.2×1019
3.2×1029

Discuss Question

Answer: Option B. -> 1.6×10−29
:
B

p = q \times (d) = 1.6 \times 10^{- 19} \times 10^{- 10} = 1.6 \times 10^{- 29} C - m

Question 28. Two charges

+ 3.2 \times 10^{- 19}

and

- 3.2 \times 10^{- 19}

C placed

2.4 ˙ A

apart form an electric dipole. It is placed in a uniform electric field of intensity

4 \times 10^{5}

volt/m. The electric dipole moment is

15.36×10−29 Coulomb×m
15.36×10−19 Coulomb×m
7.68×10−29 Coulomb×m
7.68×10−19 Coulomb×m

Discuss Question

Answer: Option C. -> 7.68×10−29 Coulomb×m
:
C
Dipole moment p = q (d)

= 3.2 \times 10^{- 19} \times (2.4 \times 10^{- 10}) = 7.68 \times 10^{- 29} C - m

Question 29. Point charges q, q, -2q are placed at the corners of an equilateral triangle ABC of side l. The magnitude of net electric dipole moment of the system is

ql
2ql
√3ql
4ql

Discuss Question

Answer: Option C. -> √3ql
:
C

Point Charges Q, Q, -2q Are Placed At The Corners Of An Equi...

P_{n e t} = \sqrt{p^{2} + p^{2} + 2 p p c o s 60^{\circ}} = \sqrt{3} p = \sqrt{3} q l

(∵ p = q l)

Question 30. There is an electric field E along X-direction. If the work done on moving a charge 0.2 C through a distance of 2m along a line making an angle