Work and Energy Test

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Work and Energy Test - 16

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Weekly Quiz Competition

Question 1
1 / -0

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 $$10\ $$$$s$$ ?

A
$$10^3\ $$$$J$$

B
$$10^4\ $$$$J$$

C
$$2\times 10^3\ $$$$J$$

D
$$4\times 10^4\ $$$$J$$

Solution

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 = $$F.s=10^4\ J$$
Question 2
1 / -0

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

A
Parallel to each other

B
Opposite to each other

C
Inclined at an angle with each other $$\theta (\neq 90^{\circ})$$

D
All of the above

Solution

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)
Question 3
1 / -0

Complete the following sentence:
The potential energy of a body is the energy by virtue of its _______ .

A
motion

B
position

C
Both A and B

D
None of these

Solution

The potential energy of a body is the energy by virtue of its position or configuration. For example, the heavy ball of a demolition machine is storing energy when it is held at an elevated position. This stored energy due to its position is referred to as potential energy. Similarly, a drawn bow is able to store energy as the result of its change of shape or configuration.
Question 4
1 / -0

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

A
mass

B
weight

C
speed

D
density

Solution

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

$$ K.E \propto m $$ & $$ K.E \propto v^2 $$
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.
Question 5
1 / -0

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

A
Work done is positive

B
Work done is negative

C
Work done is zero

D
Work done may be positive or negative

Solution

Air resistance offers retarding force opposite to the direction of instantaneous velocity. As the force acts opposite to the displacement of the body, the work done by it is negative.
Question 6
1 / -0

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

A
erg

B
dyne-cm

C
joule

D
none of these

Solution

In SI unit energy is measured in Joules.
Therefore, S.I unit of potential energy is Joule(J).
Question 7
1 / -0

Name the type of energy (kinetic energy $$K$$ or potential energy $$U$$) possessed in a compressed spring:

A
$$U$$

B
$$K$$

C
Both $$U$$ and $$K$$

D
None

Solution

When you compress a spring, it possess potential energy. The force of compression is proportional to the compression, according to Hooke's Law. Releasing the spring turns the potential energy into kinetic energy. The spring can be then used to propel some object.
Question 8
1 / -0

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

A
charge used.

B
current used.

C
power used.

D
energy used.

Solution

Electricity bill is measured in units where 1 unit is equal to kWh which is the unit of energy. Hence, when we pay for our electricity bill, we pay for the amount of electrical energy consumed by us.
Question 9
1 / -0

The commercial unit of electric energy is $$kilowatt-hour\ (kW h)$$, commonly known as:

A
$$Unit$$

B
$$Faraday$$

C
$$Curie$$

D
None of these

Solution

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.
Question 10
1 / -0

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 $$=g$$):

A
$$mgs$$

B
$$-mgs$$

C
$$0$$

D
$$2 mgs$$

Solution

Work is done only when the displacement is in the direction of force.
Work done is zero when force is perpendicular to displacement.
As the gravitational force is perpendicular to the distance moved by body, the work done by gravity will be zero.

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Work and Energy Test - 16

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Work and Energy Test - 16

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SHARING IS CARING

Question 1

$$10^3\ $$$$J$$

$$10^4\ $$$$J$$

$$2\times 10^3\ $$$$J$$

$$4\times 10^4\ $$$$J$$

Solution

Question 2

Parallel to each other

Opposite to each other

Inclined at an angle with each other $$\theta (\neq 90^{\circ})$$

All of the above

Solution

Question 3

motion

position

Both A and B

None of these

Solution

Question 4

mass

weight

speed

density

Solution

Question 5

Work done is positive

Work done is negative

Work done is zero

Work done may be positive or negative

Solution

Question 6

erg

dyne-cm

joule

none of these

Solution

Question 7

$$U$$

$$K$$

Both $$U$$ and $$K$$

None

Solution

Question 8

charge used.

current used.

power used.

energy used.

Solution

Question 9

$$Unit$$

$$Faraday$$

$$Curie$$

None of these

Solution

Question 10

$$mgs$$

$$-mgs$$

$$0$$

$$2 mgs$$

Solution

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