# Test: Work & Energy

## 10 Questions MCQ Test Engineering Mechanics | Test: Work & Energy

Description
Attempt Test: Work & Energy | 10 questions in 10 minutes | Mock test for NEET preparation | Free important questions MCQ to study Engineering Mechanics for NEET Exam | Download free PDF with solutions
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

### 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: 3

### 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: 4

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: 5

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: 6

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: 7

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: 8

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.
QUESTION: 9

A machine gun fires 60 bullets per minute, with a velocity of 700 m/s. If each bullet has a mass of 50g, find the power developed by the gun.

Solution:

Mass of the bullets = 60×50 = 3000g = 3kg
v = 700m/s t = 1min = 60s
Power = W/t = (Kinetic energy)/t = 12250W.

QUESTION: 10

If a force acts perpendicular to the direction of motion of a body, what is the amount of work done?

Solution:

If a force acts perpendicular to the direction of a body, the amount of work done is zero because there is no displacement in the direction of a force. Use Code STAYHOME200 and get INR 200 additional OFF Use Coupon Code