STD-IX, CBSE BOARD, NCERT BOOK, CHAPTER-11, IMPORTANT MCQs ON "POWER"

1.  ______ is defined as the rate of doing work.

(a) Energy

(b) Power

(c) Force

(d) Current

 

ANS: Power

 

2.  Power is defined as-

(a) work done per unit time

(b) mass per unit volume

(c) energy consumed per unit time

(d) both (a) and (c)

 

ANS: work done per unit time

 

3.  If work is done at a faster rate, then-

(a) power is more

(b) power is less

(c) power is not required to do the work

(d) infinite power is required

 

ANS: power is more

 

4.  Two persons A and B do equal work. They will have equal power if-

(a) time taken by A to do the work is more than the time taken by B

(b) time taken by A to do the work is less than the time taken by B

(c) time taken by both is equal

(d) power is independent of the time taken to do the work

 

ANS: time taken by both is equal

 

5.  A person X does 500 J of work in 10 minutes and another person Y does 600 J of work in 20 minutes. Let the power delivered by X and Y be P_X and P_Y respectively. Then,

(a) P_X = P_Y

(b) P_X > P_Y

(c) P_X < P_Y

(d) None of these

 

ANS: P_X > P_Y

 

6.  The ratio of change in the kinetic energy of a body to the time taken by the body for the change in energy is equal to the-

(a) pressure applied by the body

(b) work done on the body

(c) energy stored in the body

(d) power expended by the body

 

ANS: power expended by the body

 

7.  Which one of the following is not the unit of energy?

(a) joule

(b) newton metre

(c) watt

(d) kilowatt hour

 

ANS: watt

 

8.  SI unit of power is-

(a) watt

(b) joule

(c) newton

(d) metre

 

ANS: watt

 

9.  The practical unit of power is-

(a) kilowatt

(b) watt

(c) horse power

(d) kilowatt-hour

 

ANS: horse power

 

10.  Two army persons A and B each of weight 500 N climb up a rope through a height of 10 m. A takes 20 s while B takes 40 s to achieve this task. What is the ratio of powers of person A and B?

(a) 1:2

(b) 1:4

(c) 2:1

(d) 1:2

 

ANS: 2:1

 

11.  A lamp consumes 1000 J of electrical energy in 10 seconds. What is its power?

(a) 100 W

(b) 100000 W

(c) 1000 W

(d) 10000 W

 

ANS: 100 W

 

12.  If a light bulb is switched on for 20 s and it consumes 2400 J of electrical energy then its power is-

(a) 120 W

(b) 70 W

(c) 80 W

(d) 90 W

 

ANS: 120 W

 

 

13.  An elevator is designed to lift a load of 1000 kg through 6 floors of a building averaging 3.5 m per floor in 6 seconds. Power of the elevator, neglecting other losses will be-

(a) 4.33 x 10⁴ Watt

(b) 2.21 x 10⁴ Watt

(c) 5.65 x 10⁴ Watt

(d) 3.43 x 10⁴ Watt

 

ANS: 3.43 x 10⁴ Watt

 

14.  How much time will be required to perform 520 J of work at the rate of 20 W?

(a) 24 seconds

(b) 16 seconds

(c) 20 seconds

(d) 26 seconds

 

ANS: 26 seconds

 

15.  A machine performs 1820 J of work in 20 seconds. The power of machine is-

(a) 90 W

(b) 91 W

(c) 92 W

(d) 93 W

 

ANS: 91 W

 

16.  An electric heater of 1000 watt is switched on for 2 hours. The electric energy consumed by the heater is-

(a) 7200 J

(b) 7.2 x 10⁶ J

(c) 7.2 x 10⁷ J

(d) 72000 J

 

ANS: 7.2 x 10⁶ J 

(E= Pt = 1000 watt x 2 hours = 1 kW x 2 hr = 2 kW-hour = 2 x 3.6 x 10⁶ J = 7.2 x 10⁶ J )

 

17.  An electric bulb of 60 W is used for 5 hours daily. The units of energy consumed by the bulb in one day are-

(a) 0.1

(b) 0.2

(c) 0.3

(d) 3

 

ANS: 0.3

(E= Pt = 60 watt x 5 hours = 0.06 kW x 5 hr = 0.3 kW-hour)