NEET 2020 NEWS
NATIONAL LEVEL OFFLINE TEST
Work, power and energy are the widely used terms when it comes to physics. The three subtopics are interrelated and carry 4-5% of total weightage in physics with an average of 2 questions. This topic can never be ignored as it is the basic concept that provides an idea to further mechanics chapters dealt in physics. Check NEET 2020 Physics Syllabus
Physics is considered to be the toughest among the three subjects of NEET. However, a decent rank can be expected when a candidate scores above 140 marks in physics for which he/she has to attempt around 40 questions with a high accuracy rate. To score well in this section of NEET 2020 you can go through the important formulas, simple definitions, and solved questions in the article below.
Definition of the terms:
|Definition of the term work||Work is said to be done when a particular amount of force is applied to the object that helps in the movement of the object.|
|Definition of the term power||Power is nothing but the rate at which work is done.|
|Definition of the term energy||Energy is the capacity/ability of an object to do work|
The formula of the terms:
|The formula of work||Work done at a particular time can be calculated by multiplying the force exerted during the movement of the object. W = F × d|
|The formula of power||The first and only formula used for finding the power is: P = W/t (W= work done t= time taken )|
|The formula for energy||The formula used to find the potential energy of an object is: P.E. = mgh|
SI units are the terms used after finding the exact values after the calculations.
Here, θ is used to denote the angle formed between F and d.
b & a = interval the force is applied over
x = variable force
What is the relation between Joule and erg?
1 J = 10 er
Question: There are two springs with the force constant as k1 and k2 (k1＞k2). They are stretched by the same force then
i) More work is done in the first spring
ii) In both springs equal work is done
iii) Answer: (c) More work is done in case of the second spring
iv) No work is done in both the springs
Answer: (iii) More work is done in case of the second spring
Power has several meanings and definitions. According to physics, energy is defined as,
Formula to calculate power:
P = W/t
s = Distance
v = speed
Unit of power:
Question: What is the power of the engine when the velocity of the car is v, mass m, acceleration a, and external resistance R?
Answer: (ii) (R+ma)v
K= ½ mv2
The various kinds of energy are:
Question: The block of mass is subjected to a retarding force of F=0.1J/m. What would be the final kinetic energy of a block of mass if the mass of the block is 10kg and has a constant velocity of 10m/s.
Answer: (iii) 475J
Question: What is the relation between E, P, and E if E is kinetic energy, P is momentum, and V is the velocity of the particle?
Answer: (iii) P=dE/dV×dE/dt
Question: When work is done on a body by an external force,then it's
(i) kinetic energy increases
(ii) potential energy increases
(iii) Both kinetic energy and potential energy increases
(iv) Sum of the kinetic energy and potential energy remains constant
Answer: (iii) Both kinetic energy and potential energy increases
This law states that ' when there is no external force applied on a system of particles then, the momentum of such particles are conserved'.
Question: A light and a heavy body have equal momenta. Which one has greater kinetic energy?
(i) The light body
(ii) The heavy body
(iii) The kinetic energy is equal
(iv) Data is incomplete
Answer: (i) The light body
= v2 – v1/u1 – u2
Case 1: Perfectly elastic collision: This type of collision proves that relative velocities of two bodies before and after a collision are both same.
In such case,
Case 2: Inelastic collision: This type of collision proves that the value of 'e' would depend upon the extent of loss of kinetic energy during a collision process.
In such case,
In such case,
Question: The principle of conservation of linear momentum can be strictly applied during a collision between two particles provided the time of impact is
(i) Moderately small
(iv)Depends on a particular case
Answer: (i) Moderately small
An inelastic collision is a type of collision/crash where quantity momentum is conserved while kinetic energy is not conserved at any point.
E = ½ m1u12+ ½ m2u22 - ½ (m1+ m2)v2
= m1u1 + m2u2
= (m1 + m2) v
Conservation equation and Conservative force
Conservative equation of momentum:
Conservative equation of energy:
= ½ m1u12+ ½ m2u22
= ½ m1v12+ ½ m2v22
Hence, F = - (dV/dr)
Question: Let us consider that a player catches a ball of mass 150 gm moving at a rate of 20 m/s. If the process of catching is to be completed in 0.1 sec. What is the force exerted by the ball on the hands of the player?
(i) 3000 N
(ii) 300 N
(iii) 30 N
(iv) 0.3 N
Answer: (iii) 30 N
Es = ½ kx2
Question: A spring with an initial stretch of 0.20 m has a force constant 10 N/m. When the stretch is changed to 0.25 m, the increase in potential energy is
(i) 0.2 joule
(ii) 0.3 joule
(iii) 0.1 joule
Answer: (iii) 0.1 joule
Stable equilibrium: During a stable equilibrium, the conditions applied are as follows:
Unstable equilibrium: During an unstable equilibrium, the conditions applied are as follows:
Neutral equilibrium: During a neutral equilibrium, the conditions applied are as follows:
Question: An object of mass 500 g initially at rest is acted upon by a variable force whose X component varies with X in the manner shown. The velocities of the object at the point X = 8 m and X= 12m would have the respective values nearby-
i) 18 m/s and 24.4 m/s
ii) 23 m/s and 24.4 m/s
iii) 23 m/s and 20.6 m/s
iv) 18 m/s and 20.6 m/s
Answer: iii) 23 m/s and 20.6 m/s
Question: An engine pumps water through a hosepipe. Water is passing through the pipe and leaving it with a velocity of 2 ms-1. The mass per unit length of water in the pipe is 100 kg m-1. What is the power of the engine?
Answer: iv) 800W
Question: Let us consider that a particle of mass M is starting from rest undergoes uniform acceleration. If the speed acquired in time T is v, then the power delivered to the particle is
ii) ½ × Mv2/T2
iv) ½ × Mv2/T
Answer: iv) ½ × Mv2/T
Question: Let us consider that the moving block having mass m, collides with another stationary block having mass 4m. The lighter block comes to rest after collision. When the initial velocity of the lighter block is v, then the value of the coefficient of restitution(e) shall be:-
Answer: ii) 0.25
Question: A force F= 20+10y acts on a particle in redirection where F is in Newton and y is in the meter. Work is done by this force to move the particle from y= 0 to y= 1m is:
i) 20 J
ii) 30 J
iii) 5 J
iv) 25 J
Answer: iv) 25 J
Question: A shel which is initially at rest explodes into two pieces of equal mass, then the two pieces shall,
(i) Move with different velocities in different directions
(ii) Be at rest
(iii) Move with the same velocity in the same direction
(iv) Move with the same velocity in opposite directions
Answer: (if) Move with the same velocity in opposite directions
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