# MCQ : Work And Energy - 2

## 20 Questions MCQ Test Science & Technology for UPSC CSE | MCQ : Work And Energy - 2

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Attempt MCQ : Work And Energy - 2 | 20 questions in 20 minutes | Mock test for Class 9 preparation | Free important questions MCQ to study Science & Technology for UPSC CSE for Class 9 Exam | Download free PDF with solutions
QUESTION: 1

### On tripling the speed of motion of a body, the change in K.E. is:

Solution:

K.E. ∝ v2
So when v → 3v, K.E. → 9K.E.

QUESTION: 2

### The moon revolves around the earth due to the gravitational force (F) of the earth on the moon. The work done by the gravitational force is (r = radius of the circular orbit of moon):

Solution:
• The work done by the moon when it revolves around the earth is zero because here displacement of the moon and gravitational force of earth are perpendicular to each other.
• Work done (W) = F x d x cosƟ. In the case of the revolution of the moon around the earth, Ɵ is 90°. Thus, W = F x d x cos90° = F x d x 0 = 0.
• So, the work done by the moon when it revolves around the earth is Zero.
QUESTION: 3

### An electric bulb of 60 W is used for 5 hours a day. The cost of electricity involved in a month of 30 days at Rs. 3.00 per unit is (in Rs):

Solution:

Cost of Electricity = P*t*cost per kW
=0.06 kW x (5 x 30) x 3= Rs. 27

QUESTION: 4

A body is moved through a distance of 3 m in the following different ways. In which case is the maximum work done?

Solution:

Work done = Mgh
Work will be maximum when the change in height is maximum, thus when it is lifted vertically upward.

QUESTION: 5

A: 50 kg man climbing a ‘slant length of 5 m along a 30° incline.
B: 25 kg man running with 2 m/s speed.
C: A force of 5 N acting on an object moving with 5 m/s speed for 5 min.
If the energies in A, B and C are EA, EB and EC respectively, then:

Solution:

Ea = mv2/2 = 50 x 10 x 5sin30º = 250j
Eb = mv2/2 = 25 x 4/2 = 50j
Ec  = fvt = 5 x 25 x 60 = 7500j
Therefore, Eb < E< Ec

QUESTION: 6

Two bodies of equal weight are kept at heights of h and 1.5 h, respectively. The ratio of their potential energies is:

Solution:

Potential energy is mathematically defined as, P.E = mgh
Potential energy of body 1 = P.E1 = mgh1
Potential energy of body 2 = P.E2 = mgh2
Since weight of two bodies are equal, therefore, P.E1 / P. E2 =  h / 1.5 h = 2:3

QUESTION: 7

If a force of F newton moves a body with constant speed v, the power delivered by it is:

Solution:

Given: Velocity = v & Force = F
We know that work done is equal to the product of force and displacement.
W = F*d
Dividing by t on both sides then we get:
W/t = F*d/t
d/t = v ( Speed = Distance/ Time)
W/t = P (Power)
Therefore, P = F*v

QUESTION: 8

In the SI system, the unit of potential energy is:

Solution:

Potential energy is energy stored in matter. Joule is the SI unit of energy.

QUESTION: 9

A mass ‘m’ falls from a height ‘h’ any point on its path the total energy is:

Solution:
• Energy at start will be = Potential Energy = mgh
• According to the law of conservation of energy, it's total energy will be the same at all points i.e. = mgh.
QUESTION: 10

Newton-metre is the unit of:

Solution:

Work = Force * Displacement (N-m)

QUESTION: 11

If the bulbs of 60 W and 40 W are connected in series to a 220 V source the bulb which glows brighter is:

Solution:
• Two bulbs of 40 W and 60 W are connected in series to an external potential difference.
•  When two bulbs are connected in series, the current I will be the same. But the resistance varies. Higher the resistance brighter the glowing.
• P = V2 / R
⇒ P, R are inversely proportional to each other.
Hence, P40 < P60
⇒ R40 > R60
• So, the resistance of 40 W bulb is higher than the 60 W bulb. So 40 W bulb will dissipate more power and glow brighter.
QUESTION: 12

A porter with a suitcase on his head is climbing up a flight of stairs with a uniform speed. The work done by the ‘weight of the suitcase’ on the suitcase is:

Solution:

Force and displacement are in the same direction.
So, the work done is positive.

QUESTION: 13

A boy holds a mass on his stretched hand. Then:

Solution:
QUESTION: 14

Two bodies of unequal masses are dropped from a cliff. At any instant, they have equal:

Solution:

They will have the same acceleration due to gravity because it is independent of mass.

QUESTION: 15

Two masses m and 2m are dropped from a certain height ‘h’. Then on reaching the ground:

Solution:
• Since the free-falling acceleration is not dependent on mass, the final velocities of both masses are the same.
The kinetic energy = KE = mv2/2
• Hence, the kinetic energy of the heavier mass will be more.
QUESTION: 16

A person A does 500 J of work in 10 minutes and another person B does 600 J of work in 20 minutes. Let the power delivered by A and B be PA and PB respectively. Then,

Solution:

Power = P = Energy/Time​ = Work/Time
PA​= 500/10*60 ​= 0.83J/s
PB= 600/20*60 ​= 0.5J/s
P> PB

QUESTION: 17

In a collision______.

Solution:
QUESTION: 18

In the case of negative work, the angle between the force and displacement is:

Solution:
• Work done by any force is the product of the component of the force in the direction of displacement and the magnitude of displacement.
W = F.d = Fd cosθ
• When  W =−ve, it means cosθ = −ve
Therefore, θ = 180º
QUESTION: 19

One unit of electricity is consumed by,
A: P = 40 W bulb used for t = 25 hours
B: P = 20 W bulb used for t = 50 hours
Both A and B are true as, energy E in kWh is best related as:

Solution:
• In the given question, P is given in Watt and we have to calculate E in kWh. So,  we have to convert watt into kW. For this, we divide Pt by 1000.
• Therefore, E = Pt / 1000  is the correct answer.
QUESTION: 20

The work done on an object does not depend upon the______.

Solution:
• Work done by any force is the product of the force in the direction of displacement and the magnitude of displacement. The work done depends upon the force and displacement.
• W = F.d, when force and displacement are perpendicular to each other work done is zero.
• Hence work done also depends upon the angle between Force and Displacement but not on the velocity of the moving object. Use Code STAYHOME200 and get INR 200 additional OFF Use Coupon Code