Work and Energy Test

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Work and Energy Test - 32

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Weekly Quiz Competition

Question 1
1 / -0

A body is under the action of two equal and opposite forces, each of 10 N. The body is displaced by 5 m.The work done is

A
+50J

B
-50J

C
100J

D
Zero

Solution

Given
Applied forces $$F=10\ N$$
Displacement $$=5$$
As the situation given in the question,
Resultant force acting on the block $${F}{}_{net}=F+(-F)$$
Hence $${F}{}_{net}=0$$
$$W={F}{}_{net} \times displacement\\ W=0\times 5=0$$

$$\therefore$$ Work done is $$ ZERO$$
Question 2
1 / -0

The spring of the winding knob of a watch has

A
mechanical energy

B
only kinetic energy

C
only potential energy

D
kinetic or potential energy

Solution

We know that total energy is kinetic energy plus potential energy.

Now, kinetic energy is

$$E=\frac { 1 }{ 2 } M{ V }^{ 2 }$$

Which depends on velocity. In watch there is no displacement in the knob, hence velocity is zero. So there is no kinetic energy. Only potential energy is there.
Question 3
1 / -0

The energy possessed by wind is

A
kinetic energy

B
potential energy

C
thermal energy

D
sound energy

Solution

Kinetic energy is the energy possessed by an object due to its motion. The energy possessed by the wind is kinetic energy due to the motion of air.
Question 4
1 / -0

You lift a suitcase from the floor and keep it on the table. The work done by you on the suitcase depends on

A
the path taken by the suitcase

B
your weight

C
the weight of the suitcase

D
the time taken by you in doing so

Solution

The work done by a person in lifting an object is stored as its potential energy $$mgh$$.
Hence, work done depends on the weight of the object $$mg$$.
Thus option C is correct.
Question 5
1 / -0

A body at rest may have

A
speed

B
velocity

C
energy

D
momentum

Solution

The body at rest may have energy.
For example: A body put on height at rest has potential energy = mgh.
Question 6
1 / -0

The work done in lifting 1 kg mass to a height of 9.8 m is about

A
1 J

B
9.8 J

C
$$(9.8)^2 J$$

D
$$\displaystyle \frac{1}{(9.8)^2} J$$

Solution

The work done in lifting an object is stored as its potential energy.
Mass of object $$m = 1$$ kg
Height upto which it is lifted $$h = 9.8$$ m
Hence work done $$W= m g h = 1 \times 9.8 \times 9.8 = (9.8)^2 J$$
Thus option C is correct.
Question 7
1 / -0

Work done by centripetal force in revolving a satellite around the earth is

A
Zero

B
Unity

C
Infinity

D
Nothing can be decided

Solution

Centripetal force is always perpendicular to the velocity of the satellite. So work done by the centripetal force is zero.
Question 8
1 / -0

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?

A
The time required

B
Height of the table

C
Mass of the doll

D
Cost of the doll

Solution
Question 9
1 / -0

If a body moves along a frictionless horizontal surface its weight:

A
Does work

B
Does not work

C
Work partially

D
None of these

Solution

Work done by the force of gravity on an object (weight) depends on vertical displacement.
Vertical displacement, $$h = 0$$
Mass, $$m$$
Acceleration due to gravity, $$g$$
Work done, $$W = mgh$$
$$W=mg\times 0$$
$$W = 0\ J$$

$$\therefore$$ If a body moves along a frictionless horizontal surface its weight does not work.
Question 10
1 / -0

$$kg m^2s^{-2}$$ represents the unit of :

A
kinetic energy only

B
work done only

C
potential energy only

D
all the above

Solution

Work done is same as energy which is measured in joules. 1 joule is same as 1 newton expanded over 1 meter which is force multiplied by distance.
Force is defined as mass into acceleration. Hence if we accelerate 1kg mass by 1m/s$$^{2}$$ in a straight line for a distance of 1 meter, we have indirectly expanded 1 joule of energy .
Also acceleration is distance per second squared.
Thus we have (mass $$\ast$$ acceleration $$\ast$$ distance) which is Kg m$$^{2}$$ S$$^{-2}$$.

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Re-Attempt Weekly Quiz Competition

Work and Energy Test - 32

Result

Work and Energy Test - 32

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SHARING IS CARING

Question 1

+50J

-50J

100J

Zero

Solution

Question 2

mechanical energy

only kinetic energy

only potential energy

kinetic or potential energy

Solution

Question 3

kinetic energy

potential energy

thermal energy

sound energy

Solution

Question 4

the path taken by the suitcase

your weight

the weight of the suitcase

the time taken by you in doing so

Solution

Question 5

speed

velocity

energy

momentum

Solution

Question 6

1 J

9.8 J

$$(9.8)^2 J$$

$$\displaystyle \frac{1}{(9.8)^2} J$$

Solution

Question 7

Zero

Unity

Infinity

Nothing can be decided

Solution

Question 8

The time required

Height of the table

Mass of the doll

Cost of the doll

Solution

Question 9

Does work

Does not work

Work partially

None of these

Solution

Question 10

kinetic energy only

work done only

potential energy only

all the above

Solution

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