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# Test: Work & Energy

## 10 Questions MCQ Test Physics Class 11 | Test: Work & Energy

Description
This mock test of Test: Work & Energy for JEE helps you for every JEE entrance exam. This contains 10 Multiple Choice Questions for JEE Test: Work & Energy (mcq) to study with solutions a complete question bank. The solved questions answers in this Test: Work & Energy quiz give you a good mix of easy questions and tough questions. JEE students definitely take this Test: Work & Energy exercise for a better result in the exam. You can find other Test: Work & Energy extra questions, long questions & short questions for JEE on EduRev as well by searching above.
QUESTION: 1

### When a body falls freely under gravity, then the work done by the gravity is:

Solution:
• If a force acting on a body has a component in the direction of displacement, then the work done by the force is positive.
• Hence when a body falls freely under the influence of gravity the work done by gravity is positive.
QUESTION: 2

### There are two bodies X and Y with equal kinetic energy but different masses m and 4m respectively. The ratio of their linear momentum is:

Solution:

X and Y have equal kinetic energy but their masses are m and 4m respectively.
► 1/2 m1v12 = 1/2 m2v22
► mv12 = 4m * v22
► v1 : v2 = 2 : 1
Hence the ratio of their linear momentum is:
m1v1 : m2v2 = m * 2v : 4m * v = 1 : 2

QUESTION: 3

### Ram and Sham together can complete a vocation in 8 days. Ram can do likewise work all alone in 12 days. To what extent will sham take to carry out the occupation without anyone else's input?

Solution:

► (Ram + Sham)'s 1 day work = 1 / 8
► Ram 1 day work = 1 / 12
► Sham 1 day work = (1 / 8 - 1 / 12) = 1 / 24
∴ Sham alone can finish the work in 24 days.

QUESTION: 4

A truck moves at a steady speed on a horizontal road. What is the work done by the road on the truck?

Solution:

The work done is zero because while the truck does have a displacement over time, the force of the road (the normal force) is perpendicular and so the dot product of the two is zero.

QUESTION: 5

Which of the following is not a unit of energy?

Solution:
• The joule is a derived unit of energy in the International System of Units, not Joule/meter.
• It is equal to the energy transferred to an object when a force of one newton acts on that object in the direction of the force's motion through a distance of one meter.
QUESTION: 6

By how much does kinetic energy increase if the momentum is increased by 20%?

Solution:

The kinetic energy is given by:

KE= p2/2m

So, ΔKE = 2pΔp​ / 2m = pΔp / m​
ΔKE / KE ​= (pΔp/m)​ * (2m/p2)​ = 2Δp / p
Since the momentum p increases by 20%, so the final momentum becomes 1.2p.
Hence, KEfinal​ = (1.2p)/ 2m​ = 1.44p2 / 2m​ = 1.44KE
So, % change in KE = 44%

QUESTION: 7

Raindrops fall on the earth with certain kinetic energy on the earth. From where do they get this energy?

Solution:

Every object that tends to fall or does fall on earth's surface does have a gravitational acceleration which is possessed by them due to their gravitational potential energy.

QUESTION: 8

Time rate at which work is done by a force is:

Solution:

We know that Work done, W = F.s
where F is force and s is displacement due to that force.
Thus rate of work done is:

dW/dt = d(F.s)/dt

So as F is constant we get,
dW/dt = F.d(s)/dt = F.v = P (Power)

QUESTION: 9

Output of a truck is 4500 J and its efficiency is 50%, the input energy provided to the truck is:

Solution:

► η = work output / heat input​
► η = 50% = 50/100 = 1/2
► 1/2 = 4500 / Heat input
► Heat input = 9000 J

QUESTION: 10

When a body slides against a rough horizontal surface, the work done by friction is:

Solution:
• If a force acting on a body has a component in the opposite direction of displacement, the work done is negative.
• So when a body slides against a rough horizontal surface, its displacement is opposite to that of the force of friction. The work done by the friction is negative.