Work and Energy Test

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Work and Energy Test - 21

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Weekly Quiz Competition

Question 1
1 / -0

Water stored in a dam possesses:

A
no energy

B
electrical energy

C
kinetic energy

D
potential energy

Solution

The potential energy possessed by the object is the energy present in it by virtue of its position or configuration. Water stored in a dam , when allowed to flow, has kinetic energy which was earlier stored as potential energy.
Question 2
1 / -0

There are $$5$$ tube-lights each of $$40\ W$$ in a house. These are used on an average for $$5\ hrs/day$$. In addition, there is an immersion heater of $$1500\ W$$ used on an average for $$1\ hr/day$$. The number of units of electricity that are consumed in a month of $$30\ days$$ is:

A
$$25\ units$$

B
$$50\ units$$

C
$$75\ units$$

D
$$100\ units$$

Solution

$$E=n_1{ P }_{ 1 }{ t }_{ 1 }+n_2{ P }_{ 2 }{ t }_{ 2 }$$
$$E= 5 \times 40\times 5\times 30+1 \times 1500\times 30$$
$$=200\times 150+45000$$
$$E=75\ kWh$$
$$\Rightarrow E = 75\ units$$
Question 3
1 / -0

The electrical energy in kilowatt hours consumed in operating ten $$50\ W$$ bulbs for $$10\ hrs/day$$ in a month of $$30\ days$$ is

A
$$1500$$

B
$$15000$$

C
$$15$$

D
$$150$$

Solution

Let
$$n$$ be the number of bulbs, $$n= 10$$
$$P$$ be the power of each bulb, $$P= 50\ W$$
total time to burn the bulb, $$t =10 \times 30 = 300\ hr$$

Now the energy $$E$$, consumed in operating the bulbs is:
Energy consume by each built in 30 days $$E=Pt=50\times 300$$
Energy consume by 10 bulbs in 30 days $$E=nPt=10 \times 50 \times 300\ Wh$$

$$E=150\ kWh$$ (Option D)
Question 4
1 / -0

A pump delivers water at the rate of $$2400\ litres$$ in $$6\ minutes$$ over a head of $$12\ m$$. If $$g = 10 m/s^{2}$$, then its power is:

A
$$200\ W$$

B
$$800\ W$$

C
$$240\ W$$

D
$$24\ kW$$

Solution

Given,
Volume of water delivers $$V=2400\ lit$$
Mass of water deliver $$V\times d_w=2400\times 1=2.4\times 10^3\ kg$$
Time consumed $$t=6\ mint=6\times 60\ sec$$

Power of a pump is given by,
$$ P = \dfrac{mg h}{t}=\dfrac{2.4\times 10^{3}\times 10\times 12}{6\times 60} $$$$ = 800 \ W $$
Question 5
1 / -0

A man pushes a wall and fails to displace it. He does :

A
Negative work

B
Positive but not maximum work

C
Maximum work

D
No work at all

Solution

$$\textbf{Hint}$$: We know work done in displacing the object is equal to the product of the force applied on the object and the distance traveled by it in the direction of force applied. Let us apply this concept to solve the problem.
$$\textbf{Step 1}$$:
We know $$Work \quad done(W)=F.S$$
This is the work done by the man when he pushes the wall.
Given that man pushes a wall and fails to displace it so displacement is zero i.e.., $$S=0$$
$$\textbf{Step 2}$$:
$$Work \quad done(W)=F.0=0$$
So work done is zero.
Thus option (D) is correct.
Question 6
1 / -0

A car is accelerated on a leveled road and attains a velocity 4 times of its initial velocity. In this process the potential energy of the car

A
does not change

B
becomes twice to that of initial

C
becomes 4 times that of initial

D
becomes 16 times that of initial

Solution

Potential energy is the energy possessed by a body by the virtue of its height from the ground and in the given case, the car only increases its velocity 4 times but its height from the ground remains constant. Thus, the potential energy does not change.
Question 7
1 / -0

A coconut fruit hanging high in a palm tree has ......... owing to its location.

A
Free energy

B
Kinetic energy

C
Activation energy

D
Potential energy

Solution

The potential energy possessed by the object is the energy present in it by virtue of its position or configuration. So, the hanging coconut has potential energy due to its location (height).
Question 8
1 / -0

A house is fitted with ten lamps of each $$60\ W$$. Each lamp burns for $$5\ hrs$$ a day on an average. The cost of consumption in a month of $$30\ days$$ at $$2. 80$$ rupees per unit is:

A
$$Rs. 152$$

B
$$Rs. 252$$

C
$$Rs. 352$$

D
$$Rs. 452$$

Solution

Total energy spent is given by: $$E = nE'$$
where $$n:$$ number of bulbs
$$E':$$ Energy spent by each bulb
$$E' = Pt$$
$$E' = 60 \times 5 \times 30\ Wh$$

$$ E = 60 \times 5 \times 30 \times 10$$
      $$ = 9000 \times 10$$
      $$ = 90 KWh$$

Cost $$= 90 \times 2.8$$
           $$ = 28 \times 9$$
          $$ = 252 Rs$$
Question 9
1 / -0

A rain drop of mass (1/10) gram falls vertically at constant speed under the influence of the forces of gravity and viscous drag. In falling through 100 m, the work done by gravity is

A
0.98 J

B
0.098 J

C
9.8 J

D
98 J

Solution

work done = mgh
m = mass of drop = 0.1 g = 0.00001kg
g =9.8m/s
h = 100m
work done = $$0.00001 \times 9.8 \times 100$$
= 0.098 J
Question 10
1 / -0

A girl is carrying a school bag of $$3\ kg$$ mass on her back and moves $$200\ m$$ on a leveled road. The work done against the gravitational force will be ($$g = 10\ m/s^{2}$$) :

A
$$6\times 10^{3}\ J$$

B
$$6\ J$$

C
$$0.6\ J$$

D
$$Zero$$

E
None of these

Solution

The amount of work done is expressed in the equation: $$W = F.d cos\theta$$. In this case, the total work done is zero as the displacement is perpendicular to the applied force.

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Re-Attempt Weekly Quiz Competition

Work and Energy Test - 21

Result

Work and Energy Test - 21

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SHARING IS CARING

Question 1

no energy

electrical energy

kinetic energy

potential energy

Solution

Question 2

$$25\ units$$

$$50\ units$$

$$75\ units$$

$$100\ units$$

Solution

Question 3

$$1500$$

$$15000$$

$$15$$

$$150$$

Solution

Question 4

$$200\ W$$

$$800\ W$$

$$240\ W$$

$$24\ kW$$

Solution

Question 5

Negative work

Positive but not maximum work

Maximum work

No work at all

Solution

Question 6

does not change

becomes twice to that of initial

becomes 4 times that of initial

becomes 16 times that of initial

Solution

Question 7

Free energy

Kinetic energy

Activation energy

Potential energy

Solution

Question 8

$$Rs. 152$$

$$Rs. 252$$

$$Rs. 352$$

$$Rs. 452$$

Solution

Question 9

0.98 J

0.098 J

9.8 J

98 J

Solution

Question 10

$$6\times 10^{3}\ J$$

$$6\ J$$

$$0.6\ J$$

$$Zero$$

None of these

Solution

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