MCQ Questions for Class 9 Physics Work And Energy Quiz 2

The SI unit of energy is:

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newton
0%
pascal
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joule
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watt

1 kilowatt hour

$=$ ___________ .

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$10.6 \times 10^6$ Joule
0%
$3.6 \times 10^6$ Joule
0%
$30.6 \times 10^6$ Joule
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$3.6 \times 10^5$ Joule

Explanation

$1\ watt = 3600\ joule$

$1\ kW = 1000\ watt$

$1\ h=60\times 60 = 3600\ s$

$1\ kWh= 1\ kW\times 1\ hour=1000\ W\times 3600\ s = 1000 \times 3600 joule = 3.6 \times 10^{6}\ J$

Find the energy in

$kWh$ consumed in

$10$ hours by four devices of power

$500\ W$ each.

0%
$30 \:kWh$
0%
$25 \:kWh$
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$20 \:kWh$
0%
$35 \:kWh$

Explanation

Hint: Calculate the energy consumed by each device.

Correct answer is an option (C).

Step 1: Calculate energy consumed by each device

The power of each device is

$500W$ .

The time for which each device is used is

$10hr$

Energy consumed by each device

$=500\times 10$ =

$5000Wh$

$5kWh$

Step 2: Calculate energy consumed by four devices.

Energy consumed by one device

$=5kWh$

Energy consumed by four devices

$=5\times 4$

$=20kWh$

Hence, the energy consumed by four devices in $kWh$ is $20kWh$ .

The correct answer is an option (C).

Work is said to be done when:

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(i) a force should act on an object, and (ii) the object must be displaced.
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(i) no force should act on an object, and (ii) the object must be displaced.
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(i) a force should act on an object, and (ii) the object must not be displaced.
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(i) no force should act on an object, and (ii) the object must not be displaced.

The expression for work done, when the displacement is in the direction of the force is:

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$F \times S$
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$0$
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$- \dfrac{F}{ S}$
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$\dfrac{F \times S}{2}$

Explanation

In this case, the force and the displacement acts along the same direction. So, work done is positive. Therefore, the expression for work done is given as

$Work\ done=Force(F)\times Displacement(S)$ .

The CGS unit for energy is:

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dyne
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erg
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centimeter
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joule

Explanation

The CGS unit for energy is erg.

$1\ erg = 10^{-7} J$

The power output of a motor is

$5 \ kW.$ What is the work done by the motor in

$5 \ s$ ?

0%
2.5 k J
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25 kJ
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250 k J
0%
25000 k J

Explanation

Power

$=\dfrac{Work }{Time}$
So Work

$={Power}\times Time$

Given:

$P=5 \ kW$

$t= 5 \ sec$

$W=5\times 5 =25 \ kJ$

Hence, option B is correct.

The capacity of a body to do work is called ______ .

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Stamina
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Potential
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Velocity
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Energy

The rate of doing work is called ........

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power
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energy
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acceleration
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velocity

Energy can be defined as:

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The capacity to do work
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Work done in unit time
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A push or a pull
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Attraction between two oppositely charged particles

Which among the following is the commercial unit of electrical energy?

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Volt
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Watt
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Ampere
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KWh

When heated, molecules absorb ____ and their capacity to do ____ increases.

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Work ,energy
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Energy ,work
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Heat, work
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Energy ,heat

Explanation

When heated, molecules absorb the

$energy$ , and their capacity to do

$work$ increases.

When the time taken to complete a given amount of work increases, then :

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power generated increases
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power generated decreases
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energy increases
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energy decreases

Explanation

Power is the rate of energy generation(or absorption).

The relation between time and power is P =

$\dfrac{E}{t}$ .

So power and time are inversely proportional to each other. Hence when the time to complete a given amount of work increases then the power generated decreases.

Power is measured in :

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joule per second
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joule per minute
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joule per square second
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none of these

Explanation

As, Power

$=\dfrac{Energy(J)}{Time(S)}$
So, Power is measured in joule per second. It is known as

$watt$ .

Power spent by a machine depends on:

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the amount of work done by the machine
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time taken by the machine to do the work
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both A and B
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neither of A and B

Explanation

$Power= \dfrac{Work\quad done}{time \quad taken}$

Power spent by a machine depends on two factors:
(i) the amount of work done by the machine and
(ii) the time taken by the machine to do the work.
If a machine performs a given amount of work at a faster rate, more power is spent by the machine.

$1J$ of work is done in

$1s$ , the power spent is equal to:

0%
$1\ Js$
0%
$1\ MW$
0%
$1\ W$
0%
None of these

Explanation

$1\ J$ of work is done in

$1\ s$ , the power spent is said to be

$1\ W$ .

$Power = \dfrac{work}{time}$

$\Rightarrow 1\ W=\dfrac{1J}{1s}$

$\Rightarrow 1\ W=1{J}{s}^{-1}$

Unit of power is

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Hp
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Kilowatt hour
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Watt
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None

Explanation

The power of the appliance is defined as the rate of consumption of energy by the appliance.

Power,

$P = \dfrac{Energy}{time}$

The unit of power is

$Js^{-1}$ or watt

$(W)$ .

Work is expressed by the formula as

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Work $=$ Force (N) $\times$ Distance (m)
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Work $=$ Force (g) $\times$ Distance (m)
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Work $=$ Force (mg) $\times$ Distance (m)
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Work $=$ Force (kg) $\times$ Distance (cm)

For a heater rated at 4.4 KW; 220 V, calculate the energy consumed by the heater in 4 hours?

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12 KWh
0%
17.6 KWh
0%
0 KWh
0%
4.4 KWh

Explanation

Given :

$P = 4.4$ KW,

$t = 4$ h

$\therefore$ Energy consumed in 4 h

$\Rightarrow E= P\times t =4.4\times 4 = 17.6$ kWh

One megawatt is equivalent to

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$\displaystyle 10^{2}W$
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$\displaystyle 10^{6}W$
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$\displaystyle 10^{4}W$
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$\displaystyle 10^{8}W$

Explanation

Prefix Mega means

$10^6$ .

So, 1 Megawatt =

$1 \times 10^6$ W

1 Megawatt = a
1 Horsepower = b

0%
$\displaystyle a={ 10 }^{ 3 }W,b=1.34W$
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$\displaystyle a={ 10 }^{ 6 }W,b=746W$
0%
$\displaystyle a={ 10 }^{ 6 }J,b=0W$
0%
$\displaystyle a={ 10W,b={ 10 }^{ 3 }W }$

Explanation

Mathematically ,1 Megawatt

$= 10^6$ W

One horsepower is equal to 746 watt i.e

$1$ hp

$= 746$ W

An agent does

$4$ J of work in

$2$ s. Find the power of the agent.

0%
$1$ W
0%
$3$ W
0%
$2$ W
0%
$6$ W

Explanation

Given: Work done

$W=4\ J$ , time

$t=2\ s$

We know that

$Power=\dfrac{Work}{Time}=\dfrac{4}{2}=2\ W$

Practical uit of power

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kw
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mw
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gw
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hp

Explanation

Practical unit of power is horsepower

$(hp)$ .

One horsepower is equal to 746 watts.

whereas Watt is the SI unit of power.

The practical unit for the measurement of electric power is:

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watt
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kilowatt
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kilowatt hour
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horse power

Explanation

SI unit of power is $J/s \ (watt).$
Watt can be represented as $kilowatt \ (10^3$ watt).
Kilowatt hour is unit of energy (or watt sec, Kilowatt can be changed to watt and hour to sec) so this is unit of energy.
Horsepower is similarly another unit of power. But it is not very convenient to use since we are using the SI units of energy (joules) and time (seconds) to calculate power. We will have to divide the result by $746$ to obtain power in Horsepower. $(\because 1 \ HP=746 \ W)$

So, the best possible answer is watt, i.e. option A.

Which of the following will lead to a change in kinetic energy of a body?

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change in its mass
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change in its velocity
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all of the above
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none of the above

Explanation

Kinetic energy of the body

$K = \dfrac{1}{2}mv^2$

$\implies$

$K \propto m$ and

$K \propto v^2$

Thus changing either the mass of the body or its velocity will lead to a change in kinetic energy of a body.

What is potential energy?

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Energy of an object due to its position or arrangement in a system
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Energy of an object due to its nature or arrangement in a system
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Energy of an object due to its shape or arrangement in a system
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None

Which of the following is NOT a correct unit for work?

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erg
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watt
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joule
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Nm

Unit of work is

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Joule
0%
Newton
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Tesla
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None of these

Explanation

Work is defined as the product of force applied and the displacement of the object multiplied by the

$cos$ of angle between the force applied and the displacement.

Work done

$W = F s \cos\theta$

SI unit of work is Joule

$(J)$ .

State whether the given statement is True or False :

The potential energy of a free falling object decreases progressively.

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True
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False

If Rahul has done the same amount work in less time compared to Rohan then:

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Rahul has more power
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Rohan has more power
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Both Rahul and Rohan have equal power
0%
Rahul has more energy than Rohan

Explanation

The relation between power P and work W is given by

$P=W/t$ , where,

$t$ be the time

For same amount of doing work, Power

$P\propto \dfrac 1t$

$\because$ Rahul is taking less time in compare to Rohan so, Rahul has more power.

Option A

CBSE Questions for Class 9 Physics Work And Energy Quiz 2 - MCQExams.com

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Practice Class 9 Physics Quiz Questions and Answers

CBSE Questions for Class 9 Physics Work And Energy Quiz 2 - MCQExams.com

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Practice Class 9 Physics Quiz Questions and Answers

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