### Multiple Choice Questions on POWER (Physics)

**54.** Power is defined as

(a) Time taken per joule (b) work done or energy converted per meter

**(c) Work done or energy converted per unit time** (d) distance covered
per joule

**55.** Power is a measure of the

(a) Rate of change of momentum (b) force which produces motion

(c) Change of energy **(d) rate of change of energy**

**56.** We can say that one watt is defined as

**(a) Rate of work done** (b) rate of time of one second
per joule

(c) Rate of distance of one meter per joule (d) rate of work done per meter

**57.** In symbols, one watt is equal to

**(a) 1 J s ^{-1}** (b) 1 s J

^{-1}(c) 1 m J

^{-1}(d) 1 J m

^{-1}

**Explanation:** As power = work done/ time taken

Therefore, watt = J/s =
J s^{-1}

**58.** An electric iron is rated at 1000 W. Amount of heat
generated in 15 minutes is equal to

(a) 66.67 J (b) 15 KJ (c) 900 KJ **(d) None of above**

**Solution:** Power = (Energy transfer)/time

Given that Power = 1000 (this means 1000 J of energy is transferred in one second)

If time = 15 minutes = 15 * 60 = 900 seconds, then,

Energy transferred = 900 * 1000 J = 900 KJ

**59.** If a bulb uses energy of 100 J and remains on for 25 s,
power consumed by bulb will be

(a) 12 W **(b) 4 W** (c)
220 W (d) 5 W

Power = Rate of work done = Energy transferred in one second = 100 / 25 = 4 W

**60.** A filament bulb of 100 W consumes energy of 1000 J, time
taken by bulb is

(a) 900 s (b) 1100 s **(c) 10 s** (d)
100000 s

**61.** A boy walks up staircase of 20 m with a force of 600 N; time
taken by boy is 8 minutes. Power consumed by boy is

**(a) 25 W** (b) 16 W (c) 220 W (d) 110 W

Do yourself.

**Hint:** Convert 8 minutes to
seconds.

**62.** A machine is able to lift a mass of 200 kg vertically up to
height of 30 m above ground in 50 seconds. Take g = 10 ms^{-2}. Power
of machine is

(a) 0.12 kW **(b) 1.2 kW** (c)
6.0 kW (d) 300 kW

**Hint:** The body is raised
vertically up; work is done against the gravitational force= mgh. Therefore,
work done is 200 * 10 * 30. Divide by time and convert watts to kilowatts.

**63.** 3730 watts = ______hp.

(a) 1.5 (b) 2.2 (c) 3.746 **(d) 5**

**Hint: **How many watts is one
horse power?

**64.** 1.5 kW = ______ watts

**(a) 1500** (b) 150 (c) 15000 (d)
15

**Hint:** How many watts is one
kilowatt?

**65.** Name the physical quantity which is equal to the
product of force and velocity.

(a) Work (b) energy **(c) power** (d)
acceleration

**Solution**

**66.** Which of the following
is not a unit of power?

**(a)
Joule-second** (b) watt (c)
N m/s (d) horsepower

**Explanation**

Horse power is the British engineering system unit of power.

**67. **Force
exerted by bat on ball if it strikes a ball of mass 0.16 kg initially hits bat
with speed of 25 m s^{-1 }with time impact of
0.003 s is

(a) 145 N **(b) 1333.33 N** (c)
1456.7 N (d) 6543 N

**Solution:** F = p/∆t = (0.16 * 25)
/ 0.003 = 4/0.003 = 1333.33 N

**68.** Momentum
of electron having mass 9.1 × 10^{-31} kg and velocity 2.1 × 10^{7} is

**(a)
1.91 * 10 ^{-23}**

^{ }(b) 2.34 * 10

^{-23}(c) 3.11 * 10

^{-19}(d) 7.88 * 10

^{-34}

**Solution** m = 9.1 * 10^{-31} kg v = 2.0 * 10^{7} m/s p = mv

p = 9.1 * 2.1 * 10^{-31} *
10^{7} = 19.11 * 10^{-23+7} = 19.1 * 10^{-24} = 1.91 *
10^{-23 }kg m/s