Work and Energy Test

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Work and Energy Test - 17

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Weekly Quiz Competition

Question 1
1 / -0

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

A
force

B
motion

C
roughness

D
all the above

Solution

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.

$$ K.E = \dfrac{1}{2}mv^2 $$
Question 2
1 / -0

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

A
joule

B
newton metre

C
kilowatt

D
kilowatt hour
Solution
$$\textbf{Hint:}$$ 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.
Question 3
1 / -0

An electric heater is rated $$1500 \ W$$. How much energy does it use in $$10 \ hours$$ ?

A
$$25 \: kWh$$

B
$$10 \: kWh$$

C
$$15 \: kWh$$

D
$$12 \: kWh$$

Solution

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 $$\bf{15 kWh}$$.
Question 4
1 / -0

A body at maximum height possesses:

A
Kinetic energy

B
Potential energy

C
Solar energy

D
Heat energy

Solution

Potential energy is an energy that an object possesses because of its position. So at the highest position, its potential energy is maximum.
Question 5
1 / -0

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:

A
$$Rs.\ 0.25$$

B
$$Rs.\ 0.60$$

C
$$Rs.\ 1.2$$

D
$$Rs.\ 4.00$$

Solution

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, $$C=0.48\times 1.25=Rs. 0.60 $$
Question 6
1 / -0

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

A
Power

B
Average power

C
Energy

D
Average energy

Solution

The average power is the average amount of work done or energy transferred per total time.
$${P}_{average}=\dfrac{total \ work\ done}{total \ time\ taken}$$
Question 7
1 / -0

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

A
One kilo watt

B
One watt

C
One watt-second

D
One joule

Solution

One watt is defined as the energy consumption rate of one joule per second. $$1W = 1J / 1s$$.
Question 8
1 / -0

The SI unit of energy is:

A
newton

B
pascal

C
joule

D
watt

Solution

As energy is defined via work so,the SI unit for energy is the same as the unit of work that is joule (J)
Question 9
1 / -0

1 kilowatt hour $$=$$ ___________ .

A
$$10.6 \times 10^6$$Joule

B
$$3.6 \times 10^6$$Joule

C
$$30.6 \times 10^6$$Joule

D
$$3.6 \times 10^5$$Joule

Solution

$$1\ watt = 3600\ joule$$
$$1\ kW = 1000\ watt$$
$$1\ h=60\times 60 = 3600\ s$$
$$1\ kWh= 1\ kW\times 1\ hour=1000\ W\times 3600\ s = 1000 \times 3600 joule = 3.6 \times 10^{6}\ J$$
Question 10
1 / -0

Find the energy in $$kWh$$ consumed in $$10$$ hours by four devices of power $$500\ W$$ each.

A
$$30 \:kWh$$

B
$$25 \:kWh$$

C
$$20 \:kWh$$

D
$$35 \:kWh$$

Solution

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).

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Work and Energy Test - 17

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Work and Energy Test - 17

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SHARING IS CARING

Question 1

force

motion

roughness

all the above

Solution

Question 2

joule

newton metre

kilowatt

kilowatt hour

Solution

Question 3

$$25 \: kWh$$

$$10 \: kWh$$

$$15 \: kWh$$

$$12 \: kWh$$

Solution

Question 4

Kinetic energy

Potential energy

Solar energy

Heat energy

Solution

Question 5

$$Rs.\ 0.25$$

$$Rs.\ 0.60$$

$$Rs.\ 1.2$$

$$Rs.\ 4.00$$

Solution

Question 6

Power

Average power

Energy

Average energy

Solution

Question 7

One kilo watt

One watt

One watt-second

One joule

Solution

Question 8

newton

pascal

joule

watt

Solution

Question 9

$$10.6 \times 10^6$$Joule

$$3.6 \times 10^6$$Joule

$$30.6 \times 10^6$$Joule

$$3.6 \times 10^5$$Joule

Solution

Question 10

$$30 \:kWh$$

$$25 \:kWh$$

$$20 \:kWh$$

$$35 \:kWh$$

Solution

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