Physics MCQ for Various Entrance Exam


Q.1
A body remains in uniform velocity in the absence of an external force due to -

(a) conservation
(b) inertia
(c) both conservation of momentum and inertia
(d) neither conservation of momentum nor inertia

Ans. (b)
According to Newton's first law, "A body continue to be in its state of rest or of uniform motion along a straight line, unless it is acted upon by some external force to change the state.
    Inherent property of all the bodies by virtue of which they cannot change their state of rest or uniform motion along a straight line by their own is called inertia.


Q.2
The basic principle of rocket propulsion is based on -

(a) conservation of mass
(b) conservation of momentum
(c) conservation of energy
(d) Newton's third law

Ans. (d)
The rocket consists of a combustion chamber in which liquid or solid fuel is burnt. The heat of combustion raises the pressure very high inside the chamber. Therefore, hot gases (produced by combustion) are expelled from the tail of the rocket in the form of a jet with a very high exhaust velocity. Consequently the rocket rushes in the forward direction. According to Newton's third law rocket exerts an action force on the gas jet in the backward direction, while the gas-jet exerts a reactionary force on the rocket in the forward direction. The gas-jet acquires momentum in the backward direction and so the rocket acquires an equal momentum in the forward direction.


Q.3
Consider transverse waves in a stretched string, light waves and sound waves in air. The polarisation can be observed for - 

(a) light and sound waves in air
(b) sound waves in air and string waves
(c) light waves and string waves
(d) All of the above

Ans. (c)
The lack of symmetry about the direction of travel of waves is turned as the phenomenon of polarisation. Transverse waves exhibit the lack of symmetry about the direction of their propagation. Since, light waves and waves produced in string both are transverse in nature, hence they exhibit the phenomenon of polarisation. Whereas sound waves are longitudinal, hence they do not exhibit polarisation.


Q.4
If the temperature of a black body is doubled, the wavelength at which the spectral radiancy has its maximum, is - 

(a) doubled
(b) halved
(c) quadrupled
(d) unchanged

Ans. (b)


Q.5
Nuclear fusion is common to the pair -

(a) thermonuclear reactor, uranium based nuclear reactor
(b) energy production in sun, uranium based nuclear reactor
(c) energy production in sun, hydrogen bomb
(d) disintegration of heavy nuclei, hydrogen bomb

Ans. (c)
When two lighter nuclei moving at very high speeds fuse together to form a single heavier nucleus, then this phenomenon is called nuclear fusion. This process is responsible for energy production in sun and hydrogen bomb.
       The central core of hydrogen bomb is a uranium (or plutonium) fission bomb which is surrounded by a compound of lithium and heavy hydrogen (deuterium). When the fission bomb is exploded it produces such a high temperature and pressure that the heavy hydrogen nuclei come extremely close and fuse together, liberating huge energy. 


Q.6
The dimensions of the quantities in one (or more) of the following pairs are the same. Identify the pairs -

(a) Work and Power
(b) Density and Relative Density
(c) Momentum and Impulse
(d) Stress and Strain

Ans. (c)
Impulse = change in the momentum, so the dimensions of impulse and momentum are same.


Q.7
A particle is acted upon by a force of constant magnitude which is always perpendicular to the velocity of the particle. The motion of the particle takes place in a plane. It follows that - 

(a) its velocity is constant
(b) its acceleration is constant
(c) its kinetic energy is constant
(d) it does not move on a circular path

Ans. (c)


Q.8
The circular motion of a particle with constant speed is - 

(a) simple harmonic but not periodic
(b) periodic and simple harmonic 
(c) neither periodic nor simple harmonic
(d) periodic but not simple harmonic

Ans. (d)


Q.9
A car moves on a circular road. It describes equal angled about the centre in equal intervals of time. Which of the following statements about the velocity of the car is true?

(a) Magnitude of velocity is not constant
(b) Both magnitude and direction of velocity change
(c) Velocity is directed towards the centre of the circle
(d) Magnitude of velocity is constant but direction changes

Ans. (d)
Its body covers equal angles in equal time intervals of time, so its angular velocity and hence magnitude of linear velocity is constant.


Q.10
A man is sitting on the upper birth of the coach of a train, which is to be stopped on a nearby station. Man drops an apple on the open hand of his friend sitting just below the man about 2 m away. Apple will drop - 

(a) exact in the hand of his friend
(b) little away from the hand, in the direction of motion of trains
(c) little away from the hand, opposite to the direction of motion of train
(d) None of the above

Ans. (b)





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