Work and Energy Test

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Work and Energy Test - 23

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Weekly Quiz Competition

Question 1
1 / -0

Kilowatt-hour is the unit of :

A
potential difference.

B
electric power.

C
electrical energy.

D
charge.
Solution
- Kilowatt-hour $$(KWh)$$ is unit of Electrical Energy.
We know that, $$\text{Power} \times \text{time} = \text{Energy}$$
$$\Rightarrow\ \ \text{Kilo-Watt} \times \text{Hour} = \text{Energy}$$
- $$1 KWh$$ is electrical energy consumed when an electrical equipment of power $$1\ KiloWatt$$ is operated for $$1\ Hour$$.
- It is also used as commertial unit of energy in households/Buildings/Factories etc where 1 Unit of electricity is equivalent of 1KW-h of energy.
Hence, Option C is correct.
Question 2
1 / -0

When velocity of a moving object is doubled its:

A
acceleration is doubled

B
momentum becomes four times more

C
kinetic energy is increased to four times

D
potential energy is increased

Solution

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

$$ K.E \propto v^2 $$

$$ New\ K.E = \dfrac{1}{2}m(2v)^2 = 4 \times K.E$$

$$ \therefore $$ The K.E. of a body will increase to 4 times if its velocity doubles.
Question 3
1 / -0

An electric kettle is rated as $$2.5\ kW, \ 250\ V$$. Find the cost of running the kettle for two hours at $$60\ \text{paisa}/\text{unit}$$.

A
$$Rs\ 6$$

B
$$Rs\ 3$$

C
$$Rs\ 9$$

D
$$Rs\ 1$$

Solution

$$Rate=0.60 Rs/kWh$$
$$Energy=Power \times time$$
Energy consumed, $$E =2.5 \times 2 = 5\ kWh $$
Cost, $$C = 5 \times 0.60 = Rs\ 3 $$
Question 4
1 / -0

An air conditioner is rated $$240\ V, 1.5\ kW$$. The air conditioner is switched on $$8\ hrs$$ each day. What is electrical energy consumed in $$30\ days$$?

A
$$2.88\ kWh$$

B
$$360\ kWh$$

C
$$120\ kWh$$

D
$$240\ kWh$$

Solution

Energy consumed is given by:
$$E= Pt$$
$$E$$: Energy consumed
$$P$$: Power
$$t$$: Time
$$\Rightarrow E = 1.5\ kW \times 30 \times 8\ hrs$$
$$\Rightarrow E= 360\ kWh $$
Question 5
1 / -0

Unit of work in MKS system is

A
Calorie

B
Newton

C
Joule

D
Watt

Solution

MKS system: A unit system of measurement based on the metric system and having the meter of length, the kilogram of mass, and the second of time as its fundamental units.
Work = Force $$\times$$ displacement
MKS unit system,
Unit of work = N-m or joule
Option C
Question 6
1 / -0

According to the law of conservation of energy, total energy is

A
Increasing

B
Decreasing

C
Constant

D
None of these

Solution

The law of conservation of energy states that the total energy is constant in any process. Energy may change in form or be transferred from one system to another, but the total remains the same.
Question 7
1 / -0

Which of the following physical quantities is different from others?

A
Work

B
Kinetic energy

C
Force

D
Potential energy

Solution

Kinetic energy is the energy possessed by the body by virtue of its motion and potential energy is the energy possessed by the virtue of its position and shape. Energy is required to do work.
Hence work, kinetic energy, potential energy all can be measured using same unit, i.e joule.
So, force is the physical quantity here which is different from others as given by product of mass and acceleration. S.I unit of force is $$N$$ (newton).
Question 8
1 / -0

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

A
Momentum

B
Retardation

C
Kinetic energy

D
Potential energy

Solution

When a ball is projected upwards it's height increases.
As height increases, $$v$$ velocity decreases (Kinetic Energy Decreases) so Potential energy increases.
$$Potential $$ $$ Energy$$= $$mgh$$
Question 9
1 / -0

What is one unit of household electrical energy in J?

A
$$1000\ J$$

B
$$3600\ J$$

C
$$0.6 \times 10^3 J$$

D
$$3.6 \times 10^6 J$$

Solution

One unit of household is $$1\ kwh$$
$$kwh\ =$$ kilo watt hour
$$1\ \text{unit}$$$$= 1\ kWh$$
$$\Rightarrow 1\ \text{unit} =10^3 W \times 3600\ s$$
$$\Rightarrow 1\ \text{unit} = 3.6 \times 10^6 J $$
Question 10
1 / -0

A body is acted upon by a force that is proportional to the distance covered. If the distance covered is denoted by x, then work done by the force will be proportional to :

A
$$x$$

B
$$x^2$$

C
$$\displaystyle x^{\dfrac{3}{2}}$$

D
$$x^4$$

Solution

Given : $$\text{The force is proportional to the displacement}$$
$$\therefore F \propto x \Rightarrow F = kx$$

We know that $$\text{Work done}(W)=F.x$$
$$\therefore W= Fx = k.x.x=kx^2$$
So, $$W\ \propto x^2$$

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Re-Attempt Weekly Quiz Competition

Work and Energy Test - 23

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Work and Energy Test - 23

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SHARING IS CARING

Question 1

potential difference.

electric power.

electrical energy.

charge.

Solution

Question 2

acceleration is doubled

momentum becomes four times more

kinetic energy is increased to four times

potential energy is increased

Solution

Question 3

$$Rs\ 6$$

$$Rs\ 3$$

$$Rs\ 9$$

$$Rs\ 1$$

Solution

Question 4

$$2.88\ kWh$$

$$360\ kWh$$

$$120\ kWh$$

$$240\ kWh$$

Solution

Question 5

Calorie

Newton

Joule

Watt

Solution

Question 6

Increasing

Decreasing

Constant

None of these

Solution

Question 7

Work

Kinetic energy

Force

Potential energy

Solution

Question 8

Momentum

Retardation

Kinetic energy

Potential energy

Solution

Question 9

$$1000\ J$$

$$3600\ J$$

$$0.6 \times 10^3 J$$

$$3.6 \times 10^6 J$$

Solution

Question 10

$$x$$

$$x^2$$

$$\displaystyle x^{\dfrac{3}{2}}$$

$$x^4$$

Solution

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