# Class 9 Science MCQ Questions of Work, Power and Energy with Answers

570 views
in Physics

Class 9 Science MCQ Questions of Work, Power and Energy with Answers?

+1 vote
by (4.5k points)
edited by

The Class 9 Science MCQ Questions of Work, Power and Energy are recognized because of the most useful and widely applicable form of objective test elements. By preparing these MCQ Questions once after completing every topic, we are ready to attempt competitive exams easily and effectively.

Here you will find MCQ Questions for class 9 Science and answers on Work, Energy and Power which can able to understand the mechanism. They assist you in your preparations for various examinations.

Practice MCQ Questions for class 9 Chapter-Wise

1. When a body falls freely towards the earth, then its total energy

(a) increases
(b) decreases
(c) remains constant
(d) first increases and then decreases

2.  An iron sphere of mass 10 kg has the same diameter as an aluminum sphere of mass is 3.5 kg. Both spheres are dropped simultaneously from a tower. When they are lo m above the ground, they have the same.

(a) acceleration
(b) momenta
(c) potential energy
(d) kinetic energy

3. The work done on an object does not depend upon the

(a) displacement
(b) force applied
(c) angle between force and displacement
(d) initial velocity of the object

4. The number of joules contained in 1 kWh is

(a) $36\times10^5\;J$
(b) $3.6\times10^7\;J$
(c) $36\times10^8\;J$
(d) $3.7\times10^7\;J$

5. If speed of a car becomes 2 times, its kinetic energy becomes

(a) 4 times
(b) 8 times
(c) 16 times
(d) 12 times

6. One-joule work is said to be done when

(a) a force of 1 N displaces a body by 1 cm
(b) a force of 1 N displaces a body by 1 m
(c) a force of 1 dyne displaces a body by 1 m
(d) a force of 1 dyne displaces a body by 1 cm

7. Mechanical energy of a body includes

(a) kinetic energy only
(b) potential energy only
(c) kinetic energy and potential energy
(d) none of these

8. ……….. is defined as the rate of doing work.

(a) Power
(b) Energy
(c) Current
(d) Electric current

9. Work done by centripetal force is

(a) $>0$
(b) $\geq0$
(c) $<0$
(d) 0

10. If work is done at a faster rate, then

(a) power is more
(b) No power is required to do work
(c) power is less
(d) Infinite power is required

11. Moon revolves around the earth due to gravitational force (F) of earth on moon. The work done by the gravitational force is (r = radius of the circular orbit of moon)

(a) $F.2\pi r$
(b) $F.\pi r$
(c) zero
(d) negative work

12. The energy possessed by an oscillating pendulum of a clock is

(a) kinetic energy
(b) potential energy
(c) restoring energy
(d) mechanical energy

13. On tripling the speed of motion of a body, the change in K.E. is

(a) 9 times
(b) 8 times
(c) 4 times
(d) 2 times

14. A body at rest can have:

(a) Energy
(b) Power
(c) Momentum
(d) Velocity

15. A flying airplane possesses

(a)Only potential energy
(b) Only kinetic energy
(c) Both potential and kinetic energy
(d) None of these

16. The kinetic energy of a body is increased most by doubling its:

(a) Speed
(b) Density
(c) Weight
(d) Mass

17. In winters, rubbing of hands together for some time, causes a sensation of warmth mainly because of

(a) heat caused by the force of friction
(b) heat caused by the momentum
(c) heat caused by the motion
(d) heat flows from the blood to skin

18. The commercial unit of energy consumption in households, industries and commercial establishments is

(a) Joule
(b) Watt
(c) kW
(d) KW h (kilowatt-hour)

19. In Force vs Displacement graph, What does the area under the curve represents :

(a) Velocity
(b) Acceleration
(c) Force
(d) Work done

20. The person will have maximum Potential Energy, when?

(a) he is sleeping on the ground
(b) he is sitting on the ground
(c) he is sleeping on the bed
(d) he is standing on the roof

+1 vote
by (4.5k points)

1. Answer : (c) remains constant

Explanation: Since, the total energy of the system is always conserved, so when a body falls freely towards the earth, then its total energy remains constant i.e.the sum of the potential energy and kinetic energy of the body would be the same at all points.

Explanation: When both spheres are dropped simultaneously from a tower, then they have same acceleration because during free-fall acceleration of the body becomes equals to acceleration due to gravity. The acceleration due to gravity depends on mass of earth and the radius of earth. Hence, The acceleration will be same.

3. Answer : (d) initial velocity of the object

Explanation: Here, F= force applied on the object, d= displacement, and 0 is the angle between force and displacement. So, the work done on an object does not depend upon the initial velocity of the object.

4. Answer : (a) $36\times10^5\;J$

Explanation: One kilowatt-hour is equivalent to the energy of 1,000 joules used for 3,600 seconds or 3.6 million Joules. In equation form: 1 kWh = 3.6 million J.

5. Answer : (a) 4 times

Explanation:  The change in the kinetic energy of the object as the speed changes is proportional to the square of the factor by which the speed changes. For example, if the speed of the object becomes double, its kinetic energy changes to four times the initial kinetic energy.

6. Answer : (b) a force of 1 N displaces a body by 1 m

Explanation: 1 Joule is the amount of work done when a force of 1 Newton displaces a body through a distance of 1m in the direction of the force applied.

7. Answer : (c) kinetic energy and potential energy

Explanation: Mechanical Energy of a body includes both kinetic energy and potential energy.

Explanation:  power is the rate of doing work. It is the amount of energy consumed per unit of time.

Explanation: Work done by a centripetal force is always zero as centripetal force always act perpendicular to the direction of motion.

10. Answer : (a) power is more

Explanation: $Power=\frac{Work}{time}$

If work is done faster, power is higher. If work is done slower, power is smaller.

Explanation: The moon is revolving around the earth. In this process, the work done by the gravitational force is zero because the displacement of the moon is at the right angle to the gravitational force.

12. Answer : (d) mechanical energy

Explanation:  The energy possessed by an oscillating pendulum of a clock is the sum of potential energy and kinetic energy and this sum is known as mechanical energy.

13. Answer : (a) 9 times

Explanation: The Kinetic Energy is increased by a factor of 9 if the velocity is tripled.

Explanation: A body at rest can have energy, i.e. potential energy, or momentum. Energy is the ability to do work. The Law of conservation of energy: Energy can neither be created nor be destroyed, only Energy can be converted from one form to another.

15. Answer : (c) Both potential and kinetic energy

Explanation:  An airplane flying has both kinetic and potential energy because it is in motion due to which it has kinetic energy and it is flying at some height from the earth's surface due to which it has potential energy also.

Explanation:  If the speed of an object is doubled by increasing its velocity, its kinetic energy becomes four times its initial value. Thus kinetic energy increases by four times when its momentum is doubled. Hence kinetic energy of a body is increased most by doubling its speed.

17. Answer : (a) heat caused by the force of friction

Explanation:  That warmth is caused by a force called friction. When objects like your hands come in contact and move against each other, they produce friction. Friction happens when you overcome the resistance of one object rubbing against the other. Rub them together and there's friction.

18. Answer : (d) KW h (kilowatt-hour)

Explanation: The energy used in households, industries, and commercial establishments are usually expressed in kilowatt hour 1 kWh.

19. Answer : (d) Work done

Explanation: The area under the force-displacement curve represents the work done. It is the distance (s) of the object displaced by the application of the force (f).

20. Answer : (d) he is standing on the roof

Explanation:  Potential energy is the multiplication of mass, acceleration due to gravity and height of the object. So, the maximum potential energy at height. Hence, The person will have maximum potential energy when he is standing on roof.