Work And Energy Test

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Work And Energy Test - 3

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Weekly Quiz Competition

Question 1
1 / -0

The work is said to be done, when

A
a force is acted on the object.

B
an object is displaced.

C
a force is acted on the object and it is displaced.

D
all the above

Solution

Work is done whenever a force acts on a body and the body moves in the direction of the force.
Question 2
1 / -0

The formula to calculate work done `W` is

A
W = force x distance

B
W =

C
W =

D
none of these

Solution

Work is said to be done when a force acts on an object and it is displaced.
So,
Work = Force (F) × Distance (d)
Question 3
1 / -0

Which of the following statements is correct for a freely falling body?

A
Its kinetic energy remains unchanged.

B
Its potential energy remains unchanged.

C
Its potential energy is increased and kinetic energy is decreased.

D
Its kinetic energy is increased and potential energy is decreased.

Solution

When a body is falling freely, its potential energy is converted into kinetic energy. Therefore, its kinetic energy is increased and potential energy is decreased.
Question 4
1 / -0

What is the angle between displacement and the force applied when the work done is maximum?

A
0^o

B
45^o

C
60^o

D
90^o

Solution

Formula used to find the work done is
Work done (W) = Force (F) × displacement (d) × Cos Ѳ
When the value of Cos Ѳ is 1, the value of work done is maximum.
So, Cos Ѳ = 1
Cos Ѳ = Cos 0 (because Cos 0 = 1)
Ѳ = 0 ̊
Question 5
1 / -0

Which of the following is vector quantity?

A
Energy

B
Potential energy

C
Kinetic energy

D
None of the above

Solution

They all are scalar quantities.
Question 6
1 / -0

Which of the following statements is correct?

A
The units of kinetic energy and potential energy are different.

B
The work done and energy has same units.

C
N/m is the unit of work.

D
All are correct.

Solution

1. Kinetic energy= ½ m v² = kgm²/s²Potential energy = mgh = kgm²/s²

So, both the units are same.

2. Work = F × d = Nm = (kg m / s²) × m = kgm²/s² (Because 1N = kg m / s²)

The units of energy are kgm²/s².

Therefore, the units of work and energy are the same.

3. The unit of work is Nm.
Question 7
1 / -0

If an object of mass 1 kg is lifted to a vertical height of 1 m, work done is

A
1 J

B
9.8 J

C
980 J

D
0.98 J

Solution

Mass of the body (m) = 1 kg

Acceleration (a) = 9.8 m/s²(due to gravity)

Height (Displacement) (d) = 1m

Now, force = m × a = 1 kg × 9.8 m/s²= 9.8 N

Therefore, work done = force (f) × displacement (d) = 9.8 N × 1 m = 9.8 Nm

Work done = 9.8 J (1J = 1 Nm)
Question 8
1 / -0

A stone of mass m falls from a vertical distance h, the decrease in gravitational potential energy is

A

B

C
mgh

D

Solution

Mass of the stone = m
Vertical distance, i.e. height = h
Potential energy = mgh
= mgh
Hence, (iii) is correct.
Question 9
1 / -0

Two bodies of equal mass move with uniform velocities of V and 2V, respectively. Find the ratio of their kinetic energies.

A
1 : 1

B
2 : 1

C
1 : 4

D
4 : 1

Solution

Mass of body = m₁ = m Velocity of m₁ = v
Mass of body = m₂ = m Velocity of m₂ = 2v
Ratio of kinetic energies = k₁/ k₂= ½ m₁v²/ ½ m₂(2v)²= ½ mv²/ ½ m4v²= 1/4
Therefore, k₁ : k₂ = 1 : 4
Question 10
1 / -0

What must be the velocity (in ms^-1) of a moving body of mass 2 kg, which possesses a kinetic energy of 16 J?

A
2

B
3

C
4

D
None of the above

Solution

Mass of body = 2 kg

Velocity of body = ? m/s

Kinetic energy = 16 J = 16 kgm²/s²

Kinetic energy = ½ mv²

16 = ½ mv²

16 = ½ × 2 × v²

16 = v²

4²= v² => V = 4 m/s
Question 11
1 / -0

Calculate the work done in lifting 100 kg of water through a vertical height of 3 meter. (Assuming g = 10 m/s²)

A
4000 J

B
12000 J

C
3000 J

D
300 J

Solution

Vertical height (Displacement) (d) = 3 metre

Mass of water (m) = 100 kg

Acceleration (a) = g = 10 m/s²

Work done = F × d

W = m × a × d

W = 100 × 10 × 3

W = 3000 Nm = 3000 J ( 1 Nm = 1 J)
Question 12
1 / -0

A dry cell converts one form of energy into another.Which of the following options depicts the two forms?

A
Chemical energy into electrical energy.

B
Electrical energy into chemical energy

C
Solar energy into chemical energy

D
Solar energy into electrical energy

Solution

A dry cell converts chemical energy into electrical energy.
Question 13
1 / -0

Which of the following statements is not true?

A
At thermal power station, chemical energy of coal is changed into heat energy, which is further changed into electrical energy.

B
One form of energy can be transformed into another.

C
Different forms of energy can be measured in different units.

D
Energy and work done have the same units.

Solution

All forms of energy have the same units. Hence, option (3) is incorrect.
Question 14
1 / -0

Which of the following physical quantities has its units Watt?

A
Energy

B
Power

C
Force

D
None of these

Solution

Power = work done / time

Power = J/s = 1 Watt (Because 1 J/s = 1 Watt)
Question 15
1 / -0

Which of the following options is correct?

A
1 watt = 1 Joule × 1second

B
1 watt = 1 Joule per second

C
1 watt × 1 Joule = 1 second

D
1 watt × 1 Joule × 1 second = 1

Solution

Power = work done / time

Power = J/s = 1 Watt (Because 1 J/s = 1 Watt)
Question 16
1 / -0

How much work is done when a force of 2 N moves a body through a distance of 10 cm in the direction of force?

A
200 J

B
0.02 J

C
0.2 J

D
20 J

Solution

Displacement (d) = 10 cm = 0.1 m (Because 1 cm = 0.01 m)

Force (F) = 2 N

Work done = F × d

W = 2 × 0.1m

W = 0.2 Nm = 0.2 J (1 Nm = 1 J)
Question 17
1 / -0

A ball of mass 200 g falls from a height of 5 m. What is its kinetic energy, when it just reaches the ground? (g = 9.8 m/sec²)

A
9.8 J

B
980 J

C
4.9 J

D
None of these

Solution

Mass of the ball (m) = 200 g = 0.2 kg (Because 1g = 0.001 kg)
Height h = 5 m
Initial velocity, u = 0
We know that,
v²- u² = 2gs
v² - 0 = 2 × 9.8 × 5
v² = 98
Kinetic energy = ½ × m × v²
= ½ × 0.2 × 98 = 9.8 Joule
Question 18
1 / -0

Two bodies A and B of equal masses are kept at height of h and 2h respectively. What will be the ratio of their potential energies?

A
1: 2

B
2: 1

C
4: 1

D
1: 4

Solution

Mass of body = m₁ = m Height of m₁ = h

Mass of body = m₂ = m Height of m₂ = 2h

Ratio of potential energy = P₁/ P₂= m₁gh/m₂g (2h)= mgh/2mgh= 1/2

Therefore, P₁ : P₂ = 1 : 2
Question 19
1 / -0

What is the power of an engine which is capable of doing 10,000 J of work in 10 minutes?

A
1,000 W

B
166 W

C
16.6 W

D
60,000 W

Solution

Work done = 10,000 J

Time = 10 minutes = 10 × 60 sec = 600 s (Because 1 minute = 60 seconds)

Power = Work done/Time = 10,000/600 = 16.6 Watt
Question 20
1 / -0

When we compress a coil spring, the elastic potential energy

A
increases

B
decreases

C
disappears

D
remains unchanged

Solution

When a coil spring is compressed, the elastic potential energy is increased.

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Work And Energy Test - 3

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Work And Energy Test - 3

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Question 1

a force is acted on the object.

an object is displaced.

a force is acted on the object and it is displaced.

all the above

Solution

Question 2

W = force x distance

W =

W =

none of these

Solution

Question 3

Its kinetic energy remains unchanged.

Its potential energy remains unchanged.

Its potential energy is increased and kinetic energy is decreased.

Its kinetic energy is increased and potential energy is decreased.

Solution

Question 4

0o

45o

60o

90o

Solution

Question 5

Energy

Potential energy

Kinetic energy

None of the above

Solution

Question 6

The units of kinetic energy and potential energy are different.

The work done and energy has same units.

N/m is the unit of work.

All are correct.

Solution

Question 7

1 J

9.8 J

980 J

0.98 J

Solution

Question 8

mgh

Solution

Question 9

1 : 1

2 : 1

1 : 4

4 : 1

Solution

Question 10

2

3

4

None of the above

Solution

Question 11

4000 J

12000 J

3000 J

300 J

Solution

Question 12

Chemical energy into electrical energy.

Electrical energy into chemical energy

Solar energy into chemical energy

Solar energy into electrical energy

Solution

Question 13

At thermal power station, chemical energy of coal is changed into heat energy, which is further changed into electrical energy.

One form of energy can be transformed into another.

0^o

45^o

60^o

90^o