Work and Energy Test

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Work and Energy Test - 33

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Weekly Quiz Competition

Question 1
1 / -0

A wound watch spring has ______ energy.

A
Mechanical

B
Kinetic

C
Potential

D
Kinetic and potential

Solution

The energy possessed by a body due to its change in position or shape is called the potential energy. A wound watch has potential energy.
Question 2
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
the height of the table

C
the power she could deliver

D
cost of the doll or the table

Solution

Work done, W = force × displacement = mg × h = mgh
This is the potential energy.
If weight (mg) is known, then we need to know the height(h) of the table.
Question 3
1 / -0

If the speed of a motor car becomes six times, then the kinetic energy becomes

A
6 times

B
36 times

C
12 times

D
24 times

Solution

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

If speed becomes 6 times, then
New K.E = $$\dfrac{1}{2}$$m (6v)$$^{2}$$ = $$\dfrac{1}{2}$$m x 36 v$$^{2}$$ = 36 x ($$\dfrac{1}{2}$$mv$$^{2}$$) = 36 x K.E

Hence, kinetic energy becomes 36 times.
Question 4
1 / -0

The flowing water of a river primarily possesses ______ energy.

A
gravitational

B
potential

C
electrical

D
kinetic

Solution

Kinetic energy is where the energy is stored due to the motion of mass. When the water is at rest it possess potential energy. But in river as water keeps on flowing continuously the potential energy stored in water is converted into kinetic energy.
Hence the flowing water of a river possesses kinetic energy.
Question 5
1 / -0

When a body moves with a constant speed along a circle, then which of the following is correct :

A
no force acts on it

B
its velocity remains constant

C
no work is done on it

D
no acceleration is produced in it

Solution

If the speed is constant then no force is acting in tangential direction. Only force acting is perpendicular to direction of velocity. Hence, work done will be zero.
Question 6
1 / -0

Two bodies of equal weight are kept at heights of h and 1.5 h respectively. The ratio of their P.E. will be :

A
3: 2

B
2: 3

C
1: 1

D
none of these

Solution

$$\underline{\text{First body:}}$$
Mass of the body = $$m$$
Height at which the body is kept = $$h$$
Potential energy of the body $$U_1=mgh$$

$$\underline{\text{Second body:}}$$
Mass of the body = $$m$$
Height at which the body is kept = $$1.5h$$
Potential energy of the body $$U_2=1.5mgh$$

The ratio of potential energy is $$U_1:U_2=1:1.5=\dfrac{2}{3}=2:3$$
Question 7
1 / -0

A body rolling down a hill has :

A
K.E. only

B
P.E. only

C
neither K.E. nor P.E.

D
both K.E. and P.E

Solution

A ball rolling down a hill has both Kinetic and potential energy. Kinetic energy is due to motion. So if the ball is rolling down it has kinetic energy. Potential energy is the stored energy which is waiting to be used. If the ball is at a greater height it will have more potential energy. So when the body starts rolling the stored potential energy gets converted into kinetic energy which causes its motion. Hence a body rolling down a hill has both K.E and P.E
Question 8
1 / -0

Kilowatt hour (kWh) represents the unit of :

A
power

B
impulse

C
momentum

D
energy

Solution

1 kW h = 1 kW ×1 h = 1000 W × 3600 s = 3600000 J = 3.6 $$\ast$$ 10$$^{6}$$ J
The energy used in households, industries and commercial establishments are usually expressed in kilowatt hour.
Question 9
1 / -0

The unit of power is:

A
watt per second

B
joule

C
kilo joule

D
watt

Solution

Unit of energy is Joule (J).
Power is energy per unit time J/s. Called watt.
So option A not unit of power as unit of power is watt so watt per second can not be unit of power.
Option B is unit of energy.
Option C is also unit of energy. =$$10^3$$J.
Option D is unit of power.
So only correct option is option D.
Question 10
1 / -0

A ball of mass $$200 g$$ falls from a height of $$5 m$$. What is its K.E. when it just reaches the ground ?

A
$$9.8 J$$

B
$$98 J$$

C
$$980 J$$

D
None of these

Solution

Given,
$$M=200\ g=.2\ kg,\ \ \ \ \ \ h=5m$$
From conservation of energy,
Gain in kinetic energy $$K.E =$$ loss in $$P.E$$
initial P.E $$=$$mgh
initial K.E $$=0$$
final P.E $$=0$$
$$K.E_f-K.E_i=P.E_i-P.E_f$$
$$K.E_f-0=0.2 \times 9.8\times 5-0\\K.E_f =9.8\quad J$$

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Re-Attempt Weekly Quiz Competition

Work and Energy Test - 33

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Work and Energy Test - 33

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SHARING IS CARING

Question 1

Mechanical

Kinetic

Potential

Kinetic and potential

Solution

Question 2

the time required

the height of the table

the power she could deliver

cost of the doll or the table

Solution

Question 3

6 times

36 times

12 times

24 times

Solution

Question 4

gravitational

potential

electrical

kinetic

Solution

Question 5

no force acts on it

its velocity remains constant

no work is done on it

no acceleration is produced in it

Solution

Question 6

3: 2

2: 3

1: 1

none of these

Solution

Question 7

K.E. only

P.E. only

neither K.E. nor P.E.

both K.E. and P.E

Solution

Question 8

power

impulse

momentum

energy

Solution

Question 9

watt per second

joule

kilo joule

watt

Solution

Question 10

$$9.8 J$$

$$98 J$$

$$980 J$$

None of these

Solution

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