Work and Energy Test

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Work and Energy Test - 42

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Question 1
1 / -0

Does the Law of Conservation of energy apply to machines?

A
No, as machines require a constant input of energy in order to work

B
Yes, the energy required to maintain motion is balanced by the energy lost to friction

C
No, as machines can create energy from motion

D
Yes, but only to perpetual motion machines

E
No, as the law would apply to only perpetual motion machines

Solution

Machines require input work to be done on them, which increases the potential, or kinetic energy, or both, of the system.

However this work is done on the machines by external systems that utilize their energies to convert them to work.
So even though Law of Conservation of Energy holds for the entire system as a whole, it does not stand for the machines alone.
Question 2
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Identify which of the following option best describe work.

A
a form of energy

B
measured in Coulombs

C
the potential charge of a particle

D
equal to the voltage

E
the same for all charge collections

Solution

The energy possessed by an object is measured in terms of its capacity of doing work.Work done is converted into energy.This work done is given by:
$$WORK=FORCE\times DISPLACEMENT$$
Hence, work is a form of energy.It's SI unit is same as energy , that is $$Joule$$.
Question 3
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A man with a box on his head is climbing up a ladder. What work is said to be done by the man on the box?

A
Positive

B
Negative

C
Zero

D
Undefined

Solution

When man is climbing up a ladder by keeping box in hand, its mean that Box is also moving up. During upward movement of Box, man will apply constant force on the Box in upward direction which is just greater then the weight of Box.
Because Direction of force on the box and direction of displacement of box is in same direction, So Work done by man on the box will be positive.
Question 4
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A $$3.0\ N$$ force applied on a $$0.40\ kg$$ mass makes the mass move at a constant speed of $$3.0\ {m}{s^{-1}}$$, held back by friction. In the span of it moving through $$4.0\ m$$, the net work done on the mass is:

A
$$0\ J$$

B
$$0.90\ J$$

C
$$12\ J$$

D
$$-12\ J$$

E
$$-0.90\ J$$

Solution

As the mass is moving with a constant speed, thus net external force acting on the mass is zero.
$$F_{net} = 0$$
Displacement of the mass
$$S = 4.0$$ m
Net work done on the mass
$$W_{net} = F_{net} \times S$$
$$\Rightarrow W_{net} = 0\ J$$
Question 5
1 / -0

SI unit of energy is _________ .

A
newton

B
joule

C
erg

D
metre

Solution

Joule is the SI unit of energy.
Question 6
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Find the work done by a force of $$5 N$$ in displacing a book through $$20 cm$$ along the direction of the force.

A
$$1 J$$

B
$$3 J$$

C
$$4 J$$

D
$$5 J$$

Solution

Given:
Force $$F=5\ N$$
Displacement $$ s = 20\ cm = 0.2 \ m $$
Work done = $$Force(F)\times displacement(s) $$
= $$5 \times 0.2 $$
= $$1\ J$$
The work done is positive as the book moves in the direction of the force.
Question 7
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When a stone tied to a string is whirled in a circle, what kind of work is said to be done on it by the string?

A
Positive

B
Negative

C
Zero

D
Undefined

Solution

When a stone is tied to a string and whirled in circle $$no\ work$$ is said to be done.
The string and tangent of the circle will be $$perpendicular.$$ Hence, work done is zero.
Question 8
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How much work is done in ergs in pulling a box $$2\ m$$ across a tabletop with a force of $$20\ N$$ in the horizontal direction?

A
$$40$$

B
$$4000$$

C
$$4\times 10^7$$

D
$$40\times 10^7$$

Solution

Given,
Displacement, $$s=2\ m$$
Force applied, $$F=20\ N$$

Work done, $$W=F\times s$$
$$W=20\times 2$$
$$W=40\ J$$
We know,
$$1\ J=10^7\ ergs$$
$$\therefore W=40\times 10^7$$
$$W=40\times 10^7\ ergs$$
Question 9
1 / -0

1 horse power is equal to ______ watt :

A
746

B
500

C
646

D
700
Solution
One horse power (HP) $$=550$$ foot pound per second
Also,
$$1 $$ foot $$=0.3048 \ m$$
$$1$$ pound $$=4.448 \ N $$
So, $$1 \ HP=550\times 0.3048\times 4.448 \ Nms^{-1} \simeq 746 \ Nms^{-1} $$

Since $$ 1 W=1 \ Nms^{-1}$$,
$$\Rightarrow 746 \ Nms^{-1}=746 \ watt$$

Option A is correct.
Question 10
1 / -0

Kinetic energy is present in the following:

A
Water stored in a dam

B
Stretched rubber band

C
Water released from a dam

D
Compressed spring

Solution

Whenever a body is in motion, it has kinetic energy. When water is stored in a dam it possesses potential energy and when it is released, the potential energy converts into kinetic energy helping the water to be in motion.

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Re-Attempt Weekly Quiz Competition

Work and Energy Test - 42

Result

Work and Energy Test - 42

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SHARING IS CARING

Question 1

No, as machines require a constant input of energy in order to work

Yes, the energy required to maintain motion is balanced by the energy lost to friction

No, as machines can create energy from motion

Yes, but only to perpetual motion machines

No, as the law would apply to only perpetual motion machines

Solution

Question 2

a form of energy

measured in Coulombs

the potential charge of a particle

equal to the voltage

the same for all charge collections

Solution

Question 3

Positive

Negative

Zero

Undefined

Solution

Question 4

$$0\ J$$

$$0.90\ J$$

$$12\ J$$

$$-12\ J$$

$$-0.90\ J$$

Solution

Question 5

newton

joule

erg

metre

Solution

Question 6

$$1 J$$

$$3 J$$

$$4 J$$

$$5 J$$

Solution

Question 7

Positive

Negative

Zero

Undefined

Solution

Question 8

$$40$$

$$4000$$

$$4\times 10^7$$

$$40\times 10^7$$

Solution

Question 9

746

500

646

700

Solution

Question 10

Water stored in a dam

Stretched rubber band

Water released from a dam

Compressed spring

Solution

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