Work and Energy Test

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Work and Energy Test - 40

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Weekly Quiz Competition

Question 1
1 / -0

Convert $$28.8 kJ$$ into kilo watt hour.

A
$$8 \times {10}^{-3} kwh$$

B
$$8 kwh$$

C
$$8 \times {10}^{3} kwh$$

D
None of these

Solution

We know that $$1 kWh=3.6 \times 10^6$$ $$Joules$$
$$E=28.8 \times 10^3 $$ $$ Joules$$

$$E = \dfrac{28.8 \times {10}^{3}}{3.6 \times {10}^{6}}$$
$$= 8 \times {10}^{-3} kwh$$
Question 2
1 / -0

Calculate the monthly bill if a heater of 100 watt is used at the rate of rs. 1 per unit for 1 hour daily.

A
Rs. 200

B
Rs. 6000

C
Rs. 100

D
Rs. 3

Solution

Given : $$P=0.1$$ kW $$t = 1$$ hour per day
Energy consumed per day $$E = Pt = 0.1\times 1 = 0.1$$ kWh per day
Total energy consumed per month $$E_T = 30\times 0.1 = 3$$ kWh per month
Cost of electricity $$ =Re$$ $$ 1 $$ per unit i.e per kWh
$$\therefore$$ Monthly bill $$ = Re.$$ $$1\times 3 =$$Rs. $$3$$ per month
Question 3
1 / -0

Commercial unit of energy is .......................

A
Joule

B
Volt

C
Kilowatt hour

D
Watt second

Solution

Commercial unit of electrical energy is kilowatt hour $$\left(kWh\right)$$
$$1 kwh = 3.6 \times {10}^{6} J$$
Question 4
1 / -0

What is law of conservation of energy?

A
Energy can neither be created nor destroyed. It can only be transformed from one to another.

B
Energy can only be created nor destroyed. It can only be transformed from one to another.

C
Energy can neither be created but can be destroyed. It can only be transformed from one to another.

D
None

Solution

Energy can neither be created nor destroyed. It can only be transformed from one to another is the law of conservation of energy. For example , object falling from certain height converts its potential energy to kinetic energy and at all instant total mechanical energy remains constant.
Question 5
1 / -0

An object of mass $$40\ kg$$ is raised to a height of $$5\ m$$ above ground. If the object is allowed to fall down find its kinetic energy when it is half-way down.

A
1960 J

B
980 J

C
990 J

D
1000 J

Solution

Gravitational Potential energy, $$W = mgh$$
$$h=$$ vertical displacement $$=5\ m$$
$$m =$$ Mass of object $$= 40\ Kg$$
$$g =$$ Acceleration due to gravity $$= 9.8\ ms^{-2}$$
$$Kinetic $$ $$ Energy$$ = $$Loss$$ $$in$$ $$PE$$= $$40 \times 5 \times 9.8= 1960\ J$$
For half way down$$=\dfrac{1960}{2}= 980\ J$$
At this point i.e. half way object has an equal amount of potential and kinetic energy.
Question 6
1 / -0

A weight-lifter lifts a weight of $$2000N$$ straight up to a height of $$2.25\ m$$ in $$65$$ seconds. The weight-lifter kept holding the weight at the same height for the next $$4$$ seconds before dropping it to the floor. Find out how much work did the weight lifter do while holding the weights overhead for $$4$$ seconds ?

A
$$1300\ Joules$$

B
$$3077\ Joules$$

C
$$4500\ Joules$$

D
$$8000\ Joules$$

E
No work was done

Solution

We know that work done is given by ,
$$W=F \times s $$ where $$F$$ is force $$s$$ is displacement in direction of force
while the lifter is holding the weights overhead for $$4 \ s$$ , there is no displacement , so work done $$W=F\times 0=0$$
Question 7
1 / -0

All types of energy that exist in the nature can be categorized as either kinetic or potential. Choose correct statement regarding the validity of above sentence.

A
This statement is true for thermal and and mechanical, but not elastic

B
This statement is true for all different types of energy

C
This statement is false, except in the case of mechanical energy

D
This statement is never true

Solution

There exists other types of energies such as light energy, sound energy, nuclear energy etc. which are neither kinetic nor potential.
Energies in the form of mechanical energy are categorized as either kinetic or potential energy.
Hence the given statement is false, except in case of mechanical energy.
Question 8
1 / -0

If $$120J$$ of work is done in $$2$$ minutes by a water pump, the power of the pump is:

A
$$14.4\ KW$$

B
$$240\ W$$

C
$$60\ W$$

D
$$1\ W$$

Solution

Given: Work done, $$W=120\ J$$
Time, $$t=2\ min$$
Power, $$P=\dfrac{W}{t}=\dfrac{120}{2 \times 60} = 1W$$
Question 9
1 / -0

A car standing at the top of a hill would be an example of what type of energy?

A
Kinetic

B
Topical

C
Potential

D
Beneficial

E
Residual

Solution

The car standing at the top of hill has attained a height above the ground level. Thus it has attained a gravitational potential energy given by $$mgh$$
where $$m$$ is the mass of the car,
$$g$$ is the gravitational constant,
$$h$$ is the height above ground that it has attained.
This energy can convert into the kinetic energy of the car if it starts coming down the hill, that is lose its potential energy.
Question 10
1 / -0

Find out work done by a person in pushing a box with a force of $$10\ N$$ over a distance of $$4.0\ m$$ in the direction of the force?

A
$$0.4\ J$$

B
$$4.0\ J$$

C
$$40\ J$$

D
$$400\ J$$

E
$$4000\ J$$

Solution

$$ W = F \times s= 10 \times 4=40\ J $$

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Work and Energy Test - 40

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Work and Energy Test - 40

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Question 1

$$8 \times {10}^{-3} kwh$$

$$8 kwh$$

$$8 \times {10}^{3} kwh$$

None of these

Solution

Question 2

Rs. 200

Rs. 6000

Rs. 100

Rs. 3

Solution

Question 3

Joule

Volt

Kilowatt hour

Watt second

Solution

Question 4

Energy can neither be created nor destroyed. It can only be transformed from one to another.

Energy can only be created nor destroyed. It can only be transformed from one to another.

Energy can neither be created but can be destroyed. It can only be transformed from one to another.

None

Solution

Question 5

1960 J

980 J

990 J

1000 J

Solution

Question 6

$$1300\ Joules$$

$$3077\ Joules$$

$$4500\ Joules$$

$$8000\ Joules$$

No work was done

Solution

Question 7

This statement is true for thermal and and mechanical, but not elastic

This statement is true for all different types of energy

This statement is false, except in the case of mechanical energy

This statement is never true

Solution

Question 8

$$14.4\ KW$$

$$240\ W$$

$$60\ W$$

$$1\ W$$

Solution

Question 9

Kinetic

Topical

Potential

Beneficial

Residual

Solution

Question 10

$$0.4\ J$$

$$4.0\ J$$

$$40\ J$$

$$400\ J$$

$$4000\ J$$

Solution

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