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All questions of Work, Energy and Power for NEET Exam

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 For what angle between Force and Displacement will the work done be positive?
  • a)
  • b)
  • c)
  • d)
Correct answer is option 'C'. Can you explain this answer?

Om Desai answered
  • 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.

Work done by gravitational force on a man, in lifting a bucket out of the well by rope tied to the bucket is
  • a)
    negative
  • b)
    positive
  • c)
    zero
  • d)
    infinity
Correct answer is option 'A'. Can you explain this answer?

Om Desai answered
When the man pulls the bucket outside the well the gravitational potential of the man + bucket system increases and hence the work done by the gravitational force is negative.

Time rate at which work is done by a force is
  • a)
    Power
  • b)
    Torque
  • c)
    Centrifugal Force
  • d)
    Acceleration
Correct answer is option 'A'. Can you explain this answer?

Gaurav Kumar answered
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)

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-
  • a)
    1:2
  • b)
    4:1
  • c)
    1:√2
  • d)
    1:4
Correct answer is option 'A'. Can you explain this answer?

Suresh Iyer answered
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

By how much does kinetic energy increase if the momentum is increased by 20%?
  • a)
    55 %
  • b)
    20 %
  • c)
    44 %
  • d)
    60 %
Correct answer is option 'C'. Can you explain this answer?

Hansa Sharma answered
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)2 / 2m​ = 1.44p2 / 2m​ = 1.44KE
So, % change in KE = 44%

A wheel is at rest. Its angular velocity increases uniformly and becomes 80 radian per second after 5 second. The total angular displacement is :
  • a)
    800 Red
  • b)
    400 Red
  • c)
    200 Red
  • d)
    100 Red
Correct answer is option 'C'. Can you explain this answer?

Arjun Singhania answered
As stated

if the angular velocity increases uniformly . The angular acceleration must be constant.

Hence the formula

s= ut+ 0.5 a t^2

Where.

u= initial angular velocity

a= angular acceleration (i.e = 80/5=16 rad/s^2)

S= angular displacement

t= time taken

Now.

s= 0 + 0.5 X 16*5*5 = 200

Hence angar displacement = 200 radians

Water falls from a height of 60 m at the rate of 15 kg/s to operate a turbine. The losses due to frictional force are 10% of energy. How much power is generated by the turbine?( g = 10 m/s2) [2008]
  • a)
    8.1 kW
  • b)
    10.2 kW
  • c)
    12.3 kW
  • d)
    7.0 kW
Correct answer is option 'A'. Can you explain this answer?

Arnav Iyer answered
Given, h = 60m, g = 10 ms–2, Rate of flow of water = 15 kg/s
∴ Power of the falling water = 15 kgs–1 × 10 ms–2 × 60 m = 900 watt.
Loss in energy due to friction
∴ Power generated by the turbine = ( 9000 – 900) watt = 8100 watt = 8.1 kW

 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.
  • a)
    1225 W
  • b)
    12250 W
  • c)
    122.5 W
  • d)
    122 W
Correct answer is option 'B'. Can you explain this answer?

Tejas Verma answered
Each bullet will have KE = 1/2 * 0.05 * 700 * 700 = 12250 J
So for 60 bullets the energy given by machine in 60 second = 60 x 12250 J
Hence power developed = Energy / time =60 x12250/60 =12250W
Or power = 12.250 kW.

Which of the following is not conserved in inelastic collision?
  • a)
    momentum
  • b)
    kinetic energy
  • c)
    both momentum and kinetic energy
  • d)
    neither momentum nor kinetic energ
Correct answer is option 'B'. Can you explain this answer?

Rajesh Gupta answered
In an inelastic collision, the force of reformation is not equal to the force of deformation and thus some amount of energy is lost. But still as no external force acts upon the system momentum is still conserved.

Which of the following statement is not related to conservative force?
  • a)
    Work done in closed path is zero
  • b)
    Work done is recoverable
  • c)
    Path independent
  • d)
    Path dependent
Correct answer is option 'D'. Can you explain this answer?

Krishna Iyer answered
A force is said to be conservative if the work done by or against the force on a body is independent of path followed by the body and depends only on initial and final positions.
Work done by or against the conservative force in moving a particle along a closed path is zero.

Which of the following is not a unit of energy?
  • a)
    newton meter
  • b)
    electron volt
  • c)
    joule/meter
  • d)
    kilowatt hour
Correct answer is option 'C'. Can you explain this answer?

Gargey Dudhe answered
C is correct option because energy The joule ( symbol: J) is a derived unit of energy in the International System of Units. It is equal to the energy transferred to (or work done on) an object when a force of one newton acts on that object in the direction of its motion through a distance of one metre (1 newton metreor N⋅m). pls upvote and follow me.

When a ball is allowed to fall from a height of 20 m, 40% of its energy is lost due to impact. After one impact the ball will go up to a height of
  • a)
    12 m
  • b)
    15 m
  • c)
    8 m
  • d)
    10 m
Correct answer is option 'A'. Can you explain this answer?

Lavanya Menon answered
Before the impact the KE was ½ x m x (2g x 20) = 20mg
And let say v be the velocity after impact and for height h, v2= 2gh
Thus KE = ½ mv2 = ½m2gh = ⅗ x 20mg
Thus we get mgh = 12mg
thus h = 12 m

 Frictional force is an example of
  • a)
    ectrostatic force
  • b)
    Non conservative force
  • c)
    conservative force
  • d)
    nuclear force
Correct answer is option 'B'. Can you explain this answer?

Om Desai answered
The friction is the phenomena that defines that there is a resistance which is present there between the two surfaces. This friction is applied tangentially to the surfaces in contact. Thus the main thing is that the forces on both of the surfaces act tangential to each other.

The potential energy of a system increases if work is done [2011]
  • a)
    upon the system by a n on conser vative force
  • b)
    upon the system by a conservative force
  • c)
    by the system against a non conservative force
  • d)
    by the system against a conservative force 
Correct answer is option 'D'. Can you explain this answer?

Avantika Kumar answered
Explanation:
When work is done on a system against a conservative force, the potential energy of the system increases.

- Conservative Force: A force is said to be conservative if the work done by the force on a particle moving from one point to another depends only on the initial and final positions of the particle and not on the path followed by the particle.
- Potential Energy: Potential energy is the energy possessed by a system due to the relative positions of its components. It is a scalar quantity and is measured in joules (J).

In the given options, only option D mentions work done by the system against a conservative force, which is the correct answer.

When a system does work against a conservative force, the energy is stored in the system as potential energy. This potential energy can be released later when the system returns to its original position or configuration.

For example, when a spring is compressed by an external force, the system stores potential energy. When the external force is removed, the spring returns to its original position and releases the stored potential energy.

Hence, the potential energy of a system increases when work is done by the system against a conservative force.

Select the odd one out
  • a)
    Viscous force
  • b)
    Frictional force
  • c)
    Electrostatic force
  • d)
    Air-resistance
Correct answer is option 'C'. Can you explain this answer?

Pranav Datta answered
The odd one out among the given options is option 'C', which represents the Electrostatic force.

**Viscous Force:**
- Viscous force refers to the resistance that a fluid (liquid or gas) exerts on an object moving through it.
- It is a type of frictional force that opposes the relative motion of the object and the fluid.
- Viscous force is responsible for phenomena like drag experienced by objects moving through a fluid medium.
- Examples of viscous force include the resistance experienced by a car moving through air or a boat moving through water.

**Frictional Force:**
- Frictional force is the force that opposes the motion or attempted motion of an object past another object with which it is in contact.
- It arises due to the roughness or irregularities present on the surfaces in contact.
- Frictional force plays a crucial role in our daily lives, such as walking, driving a car, or holding objects.
- It can be both advantageous (e.g., walking) and disadvantageous (e.g., wearing out of machine parts).

**Electrostatic Force:**
- Electrostatic force is the force of attraction or repulsion between charged objects.
- It arises due to the electric charge carried by the objects.
- Objects with the same charges repel each other, while objects with opposite charges attract each other.
- Electrostatic force is responsible for various phenomena such as the attraction of clothes after being dried in a dryer or the repulsion of two magnets.

**Air-Resistance:**
- Air resistance, also known as drag, is a force that opposes the motion of an object through the air.
- It is caused by the collision of air molecules with the object in motion.
- Air resistance depends on factors such as the shape and size of the object, the speed of motion, and the density of the air.
- It affects objects moving through the air, like a falling parachute or a moving car.

**Explanation:**
The odd one out is electrostatic force because it is the only option that does not involve the interaction between objects in motion or with a fluid medium. Electrostatic force is related to the interaction between charged objects, whereas the other three forces (viscous force, frictional force, and air resistance) are associated with the motion of objects through a medium (fluid or air).

A bomb of mass 4 kg explodes in air into two pieces of masses 3 kg and 1 kg. The smaller mass goes at a speed of 90 m/s. The total energy imparted to two fragments is.
  • a)
    2.4  kj
  • b)
    5.4 kj
  • c)
    5.9 kJ
  • d)
    3.8 kJ
Correct answer is option 'B'. Can you explain this answer?

Raghav Bansal answered
By conservation of momentum we get the speed of the bigger part let say, v = 1 x90 / 3
Hence we get v = 30
Thus the total KE of the system after collision is ½ (3 X 900 + 1 X 8100)
Thus KE = ½ (10800) = 5400
Now  if we apply WET to the system, as no external force has acted upon it, we get
W = ΔKE
= 5400 - 0
= 5.4 kJ

A bomb at rest on a horizontal frictionless surface explodes and breaks into three pieces that fly apart horizontally as shown below. Select all of the following statements that must be true after the bomb has exploded.
1. The total kinetic energy of the bomb fragments is the same as that of the bomb before explosion.
2. The total momentum of the bomb fragments is the same as that of the bomb before explosion.
3. The total momentum of all the bomb fragments together is zero.
  • a)
    1,2 and 3
  • b)
    1 only
  • c)
    3 only
  • d)
    2 only
Correct answer is option 'C'. Can you explain this answer?

Naina Sharma answered
So as no external force acts upon the system, we can say that momentum of the system remains conserved but as an internal force acts that explodes the bomb, the KE of the system is never conserved. But every fragment has some non zero momentum while the bomb initially has zero momentum.

For a conservative force, F is equal to
  • a)
  • b)
  • c)
  • d)
Correct answer is option 'C'. Can you explain this answer?

Pooja Shah answered
Potential energy at a point is defined in terms the amount of work done, which is defined in terms of force and thus we get potential as an integral of force applied over some position x. Hence F(x) = -dU(x) / dx which is the differentiation of potential energy wrt position.

 If a force acts perpendicular to the direction of motion of a body, what is the amount of work done?
  • a)
    Infinity
  • b)
    Constant
  • c)
    Zero
  • d)
    sinθ
Correct answer is option 'C'. Can you explain this answer?

Anjali Sharma answered
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.

A 0.5 kg ball moving with speed of 12 m/s strikes a hard wall at an angle of 30° with the wall. It is reflected with the same speed and at the same angle. If the ball is in contact with the wall for 0.25 seconds, the average force acting on the wall is[2006]
  • a)
    24 N
  • b)
    12 N
  • c)
    96 N
  • d)
    48 N
Correct answer is option 'A'. Can you explain this answer?

Ias Masters answered
Resolving the velocities in vertical and horizontal directions, resolved parts of first velocity
v cosθ perpendicular to the wall and v sinθ parallel to the wall. In the second case, they are –v sinθ & v cosθ respectively. Here, –ve sign is because direction is opposite to the earlier ones. So we see a net change in velocity perpendicular to way = v sinθ – (–v sinθ) = 2v sinθ
This change has occured in 0.25 sec, so, rate  of change of velocity
Thus, acceleration a = 48 m/sec2
Force applied = m . a = 0.5 × 48 = 24 N

The minimum velocity (in ms_1) with which a car driver must traverse a flat curve of radius 150 m and coefficient of friction 0.6 to avoid skidding is                        [AIEEE 2002]
  • a)
    60
  • b)
    30
  • c)
    15
  • d)
    25
Correct answer is option 'B'. Can you explain this answer?

Yash Ghoshal answered
**Given Data:**
Radius of the curve (r) = 150 m
Coefficient of friction (μ) = 0.6

**To Find:**
Minimum velocity (v) to avoid skidding

**Explanation:**
When a car takes a turn on a curved road, it experiences a centripetal force that keeps it moving in a circular path. This force is provided by the friction between the tires and the road surface. If the velocity of the car is too high, the friction force may not be sufficient to keep the car on the curve, resulting in skidding.

To find the minimum velocity required to avoid skidding, we need to determine the maximum value of the centripetal force that the friction force can provide.

**Step 1:**
The maximum friction force (f) that can be provided is given by the equation:
f = μN
where N is the normal force, which is equal to the weight of the car (mg).

**Step 2:**
The centripetal force (Fc) required to keep the car moving in a circular path is given by the equation:
Fc = mv²/r
where m is the mass of the car and v is its velocity.

**Step 3:**
To avoid skidding, the maximum friction force (f) should be equal to the centripetal force (Fc):
μN = mv²/r

**Step 4:**
Substituting the value of N and rearranging the equation, we get:
μmg = mv²/r
v² = μgr
v = √(μgr)

**Step 5:**
Substituting the given values of μ and r, we can calculate the minimum velocity:
v = √(0.6 * 9.8 * 150)
v = √(88.2)
v ≈ 9.4 m/s

Therefore, the minimum velocity required to avoid skidding is approximately 9.4 m/s.

**Conclusion:**
The correct option is (b) 30 m/s.

Chapter doubts & questions for Work, Energy and Power - Topic-wise MCQ Tests for NEET 2025 is part of NEET exam preparation. The chapters have been prepared according to the NEET exam syllabus. The Chapter doubts & questions, notes, tests & MCQs are made for NEET 2025 Exam. Find important definitions, questions, notes, meanings, examples, exercises, MCQs and online tests here.

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