MCQ Questions for Class 9 Physics Work And Energy Quiz 1

What is the unit of energy in food ?

0%
$Kilo$ $calorie$
0%
$Erg$
0%
$Joule$
0%
$Calorie$

Explanation

The energy stored in food is measured in

$kilo$

$calories$ .This is the unit of energy in food.

Where

$1kilo$

$calorie=4184Joules$

The form of energy present in a wound spring is:

0%
chemical
0%
heat energy
0%
magnetic
0%
mechanical

Asha lifts a doll from the floor and places it on a table. If the weight of the doll is known, what else does one need to know in order to calculate the work Asha has done on the doll?

0%
The time required
0%
Height of the table
0%
Mass of the doll
0%
Cost of the doll

When the force retards the motion of a body, the work done is:

0%
Zero
0%
Negative
0%
Positive
0%
Positive or negative depending upon the magnitude of force and displacement

$hp$ is equal to:

0%
$0.746kW$
0%
$7.46 kW$
0%
$74.6kW$
0%
$746 kW$

Explanation

The horsepower (hp) is a unit in the foot-pound-second ( fps ) or English system, sometimes used to express the rate at which mechanical energy is expended.A power level of 1 hp is approximately equivalent to

$746$

$watt(W)$ or

$0.746$

$kilowatt(kW)$ .

The total energy at the start of the free-fall of an object is?

0%
Zero
0%
Infinite
0%
$mgh$
0%
None of these

Explanation

The kinetic energy of an object at the start of the free-fall is zero because its velocity is zero. The total energy of the object is thus its potential energy which is

$mgh$ , hence option

$C$ is correct.

As an object falls, its ______ energy changes into ______ energy.

0%
Kinetic, Potential
0%
Potential, Kinetic
0%
Total, Potential
0%
Kinetic, Total

A boy held a book of 1 kg at a height of 1 metre for 60 seconds. Calculate the work done :

0%
60 J
0%
30 J
0%
15 J
0%
0

Explanation

$work done = force\times displacement$

Since the object did not move that means displacement is zero so work done is not considered to be done. Work done by the boy will be zero

Kinetic energy is present in the following:

0%
Water stored in a dam
0%
Stretched rubber band
0%
Water released from a dam
0%
Compressed spring

The force needed to produce an acceleration of

$\displaystyle 6\ { m }/{ { s }^{ 2 } }$ in a ball of mass

$4\ kg$ will be:

0%
$24\ N$
0%
$30\ N$
0%
$32\ N$
0%
$20\ N$

Explanation

Given,

Mass,

$m=4\ kg$

Acceleration,

$a=6\ m/s^2$

We know,

Force,

$F=m\times a$

$F=4\times 6$

$F=24\ N$

How much energy in kilowatt hour is consumed in operating ten 50 watt bulbs for 10 hours per day in a month (30 days)

0%
1500
0%
5000
0%
15
0%
150

Explanation

Energy consumed

$=10\times 50\times 10\times 30\times 3600 J$

$[1 Kwh=3600\times 1000J]$

$=\frac {10\times 50\times 10\times 30\times 3600}{3600\times 1000}kWh=150$

A ball is projected upwards. As it rises, there is increase in its:

0%
Momentum
0%
Retardation
0%
Kinetic energy
0%
Potential energy

Explanation

When a ball is projected upwards it's height increases.

As height increases,

$v$ velocity decreases (Kinetic Energy Decreases) so Potential energy increases.

$Potential$

$Energy$ =

$mgh$

How much work must be done by a force on

$50\$

$kg$ body in order to accelerate it from rest to

$20\ m/s$ in

$10\$

$s$ ?

0%
$10^3\$ $J$
0%
$10^4\$ $J$
0%
$2\times 10^3\$ $J$
0%
$4\times 10^4\$ $J$

Explanation

Acceleration that causes the given rise in speed in given time =

$a=\dfrac{v}{t}=\dfrac{20\ m/s}{10\ s}=2\ m/s^2$

Thus, force acting on the body =

$F=ma=100\ N$

Distance travelled in the given time =

$s=\dfrac{1}{2}at^2=100\ m$

Thus, work done in given time =

$F.s=10^4\ J$

Work is said to be done if the force and displacement are

0%
Parallel to each other
0%
Opposite to each other
0%
Inclined at an angle with each other $\theta (\neq 90^{\circ})$
0%
All of the above

Explanation

Since work done is given by

$W=Fs\ cos \theta$

1. So for parallel case

$\theta = 0^o$ and

$W=F s$

2. For opposite case

$\theta = 180^o$ and

$W=-Fs$

3. For any angle

$\theta, W = F s \ cos\theta \neq 0$

So in all above cases, we can say that work has been done.

Hence option (d)

The K.E. of a body can be increased maximum by doubling its:

0%
mass
0%
weight
0%
speed
0%
density

Explanation

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

$K.E \propto m$ &

$K.E \propto v^2$

So doubling mass will double the kinetic energy and doubling speed will make kinetic energy

$4$ times.

$\therefore$ The K.E. of a body can be increased maximum by doubling its speed.

Complete the following sentence:

The potential energy of a body is the energy by virtue of its _______ .

0%
motion
0%
position
0%
Both A and B
0%
None of these

In SI system, the unit of P.E. is :

0%
erg
0%
dyne-cm
0%
joule
0%
none of these

Name the type of energy (kinetic energy

$K$ or potential energy

$U$ ) possessed in a compressed spring:

0%
$U$
0%
$K$
0%
Both $U$ and $K$
0%
None

A ball is thrown vertically up-wards from the ground. Regarding the work done by air resistance, which of the following is correct?

0%
Work done is positive
0%
Work done is negative
0%
Work done is zero
0%
Work done may be positive or negative

When we pay for our electricity bill, we are paying for the:

0%
charge used.
0%
current used.
0%
power used.
0%
energy used.

The commercial unit of electric energy is

$kilowatt-hour\ (kW h)$ , commonly known as:

0%
$Unit$
0%
$Faraday$
0%
$Curie$
0%
None of these

Explanation

The commercial unit of electrical energy is

$kilowatt-hour\ (kWh)$ , commonly known as

$unit$ .

$1\ kW h = 1\ unit=3.6 \times 10^6 J$ . Electricity bills are calculated in the units of energy consumed.

Work done by the gravitational force on a body of mass

$m$ moving on a smooth horizontal surface through a distance

$s$ is: (Given acceleration due to gravity

$=g$ ):

0%
$mgs$
0%
$-mgs$
0%
$0$
0%
$2 mgs$

Complete the following sentence:
The kinetic energy of a body is the energy by virtue of its______ .

0%
force
0%
motion
0%
roughness
0%
all the above

Explanation

The kinetic energy of a body is the energy by virtue of its motion. This is the definition of kinetic energy. If it has motion then it will have velocity, hence kinetic energy exists.

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

What is one unit of household electrical energy in J?

0%
$1000\ J$
0%
$3600\ J$
0%
$0.6 \times 10^3 J$
0%
$3.6 \times 10^6 J$

Explanation

One unit of household is

$1\ kwh$

$kwh\ =$ kilo watt hour

$1\ \text{unit}$

$= 1\ kWh$

$\Rightarrow 1\ \text{unit} =10^3 W \times 3600\ s$

$\Rightarrow 1\ \text{unit} = 3.6 \times 10^6 J$

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

0%
joule
0%
newton metre
0%
kilowatt
0%
kilowatt hour

Explanation

$\textbf{Hint:}$ Use the relation between energy and power.

$\textbf{Explanation :}$

If Watt is unit of power then kilowatt is also the unit of power.
Work done = Force × Distance = Newton - metre, Therefore it is the unit of Work or Energy.
Energy = Power × time = kilowatt - hour, in fact it is the commercial unit of Energy.

An electric heater is rated

$1500 \ W$ . How much energy does it use in

$10 \ hours$ ?

0%
$25 \: kWh$
0%
$10 \: kWh$
0%
$15 \: kWh$
0%
$12 \: kWh$

Explanation

Correction option: C

Hint: Energy consumed = Power × Time

Explanation for correct option:

Step 1: Find the energy consumes by the electric heater.

Power rating of the heater (P) = 1500

P= 1.5 kW = 1500 W

Time for which the heater has operated (T) = 10 h

Work done = Energy consumed by the heater

∴ Energy consumed = Power × Time

Energy consumed = 1500 × 10

Energy consumed = 15000 W

Hence, the energy consumed by the heater in $\bf{10 h}$ is $\bf{15 kWh}$ .

A body at maximum height possesses:

0%
Kinetic energy
0%
Potential energy
0%
Solar energy
0%
Heat energy

An electric lamp is marked

$60\ W,\ 220\ V$ . The cost of kilo watt hour of electricity is

$Rs.\ 1.25$ . The cost of using thing lamp on

$220\ V$ for

$8\ hrs$ is:

0%
$Rs.\ 0.25$
0%
$Rs.\ 0.60$
0%
$Rs.\ 1.2$
0%
$Rs.\ 4.00$

Explanation

Given:

Power,

$P=60\ W$

Time,

$t=8\ hrs$

Energy consumed per day,

$E=Pt=60\times 8=480\ Whr=\dfrac{480}{1000}=0.48\ kW hr$
Hence total cost,

$C=0.48\times 1.25=Rs. 0.60$

The ratio of the total work done or total energy consumed to the total time taken is called:

0%
Power
0%
Average power
0%
Energy
0%
Average energy

Explanation

The average power is the average amount of work done or energy transferred per total time.

${P}_{average}=\dfrac{total \ work\ done}{total \ time\ taken}$

When a work of 1 joule is done in 1 s, the power is:

0%
One kilo watt
0%
One watt
0%
One watt-second
0%
One joule

Explanation

One watt is defined as the energy consumption rate of one joule per second.

$1W = 1J / 1s$ .

CBSE Questions for Class 9 Physics Work And Energy Quiz 1 - MCQExams.com

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Practice Class 9 Physics Quiz Questions and Answers

CBSE Questions for Class 9 Physics Work And Energy Quiz 1 - MCQExams.com

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Practice Class 9 Physics Quiz Questions and Answers

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