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Multiple choice question for engineering

Set 1

1. The internal energy change in a system that has absorbed 2kcal of heat and done 500 J of work is
a) 6400 J
b) 5400 J
c) 7900 J
d) 8900 J

View Answer

Answer: c [Reason:] As Q=∆U+W ∆U=Q-W=2×4.2×1000-500 ∆U=8400-500=7900 J

2. 110 J of heat is added to a gaseous system, whose internal energy increases by 40 J. Then the amount of external work done is
a) 150 J
b) 70 J
c) 110 J
d) 40 J

View Answer

Answer: b [Reason:] ∆Q=+110 J,∆U=+4J ∆W=∆Q-∆U=110-40=70J

3. The molar specific heat constant pressure of an ideal gas is 7R/2. The ratio of specific heat at constant pressure to that at constant volume is
a) 9/7
b) 8/7
c) 7/5
d) 5/7

View Answer

Answer: c [Reason:] Cp=7R/2 CV=CP-R=7R/2-R=5R/2 r=Cp/Cv =(7R/2)/(5R/2)=7/5

4. The change internal energy in a cyclic process is
a) Zero
b) Infinity
c) Constant
d) Unity

View Answer

Answer: a [Reason:] The chance in internal energy in a cyclic process is zero because the system returns to its initial state.

5. It is possible that the temperature of the body changes even without giving heat to it or taking heat from it. True or false?
a) True
b) False

View Answer

Answer: a [Reason:] During an adiabatic compression, temperature increases and in adiabatic expansion, temperature decreases, although no heat is given to or taken from the system in these changes.

6. The mechanical energy can be completely converted into heat energy but the whole of the heat energy cannot be converted into mechanical energy. True or false?
a) True
b) False

View Answer

Answer: a [Reason:] The whole of mechanical energy can be absorbed by the molecules of the system in the form of their kinetic energy. This kinetic energy gets converted into heat. But the whole of the heat energy cannot be converted into work as a part of it is always retained by the system as its internal energy

7. Which statement is incorrect?
a) All reversible cycles have same efficiency
b) Reversible cycle has more efficiency than an irreversible one
c) Carnot cycle is a reversible one
d) Carnot cycle has the maximum efficiency of an the cycles

View Answer

Answer: a [Reason:] Work done per cycle = Area of the loop representing the cycle As different reversible cycles may have different loop areas, their efficiencies will also be different.

8. Which is an intensive property?
a) Volume
b) Mass
c) Refractive index
d) Weight

View Answer

Answer: c [Reason:] An intensive property is that which does not depend on the quality of matter of the system. Refractive index is an intensive property. Volume, mass and weight are extensive properties.

9. The latent heat of vaporisation of water is 2,240 J. If the work done in the process of vaporisation of 1g is 168 J, then the increase in internal energy is
a) 2408 J
b) 2240 J
c) 2072 J
d) 1904 J

View Answer

Answer: c [Reason:] From the first law of thermodynamics, dQ = mL = dU + dW dU = m L – dW = 1×2240-168 dU = 2072 J

10. If the amount of heat given to a system is 35 J and the amount of work done by the system is -15J and the amount of work done by the system is -15J, then the change in the internal energy of the system is
a) -50J
b) 20J
c) 30
d) 50J

View Answer

Answer: d [Reason:] ∆Q=∆U+∆W 35=∆U+15 ∆U=35+15=50J

11. Assertion: Reversible systems are difficult to find in real world [Reason:] Most process is dissipative in nature
a) Both assertion and reason are true and reason is correct explanation of the assertion
b) Both assertion and reason are true but reason is not correct explanation of the assertion
c) Assertion is true but reason is false
d) Both assertion and reason are false

View Answer

Answer: a [Reason:] Both the assertion and reason are true. The energy consumed is doing work against dissipative forces cannot be recovered.

12. The change in internal energy, when a gas is cooled from 927° to 27°, is
a) 100%
b) 300%
c) 200%
d) 75%

View Answer

Answer: d [Reason:] U=nCv T ∆U/U×100=∆T/T×100 ∆U/U×100=(1200-300)/1200×100=9/12×100=75%

13. During adiabatic compression of a gas, its temperature
a) Falls
b) Remains constant
c) Rises
d) Becomes zero

View Answer

Answer: c [Reason:] The work done on the gas during adiabatic process increases its internal energy and hence its temperature rises.

Set 2

1. A train is approaching with velocity 25m/s towards a pedestrian standing on the track, frequency of horn of train is 1 kHz. Frequency heard by the pedestrian is (v=350m/s)
a) 1077Hz
b) 1167Hz
c) 985Hz
d) 945Hz

View Answer

Answer: a [Reason:] γ=v/(v-vs)×γ=350/(350-25)×1000Hz =1077Hz

2. A person is standing on a railway platform and a train is approaching to him, what is maximum wavelength of sound he can hear? Wavelength of whistle=1m, speed of sound in air=330m/s, speed of train=36km/h
a) 1m
b) 32/322m
c) 33/32m
d) 12/13m

View Answer

Answer: b [Reason:] As γ=v/(v-vs)×γ vs=36km/h=10m/s ʎ=(v-vs)/v×ʎ=(330-10)/330×1=32/33 m

3. The source of sound generating of frequency of 3 kHz reaches an observer with a speed of 0.5 times the velocity of sound in air. The frequency heard by the observer is
a) 1 kHz
b) 3 kHz
c) 4 kHz
d) 6 kHz

View Answer

Answer: d [Reason:] γ=v/(v-vs)×γ =v/(v-0.5γ)×3kHz=6kHz

4. A car sounding its horn at 480Hz moves towards a high wall at a speed of 20m/s, the frequency of the reflected sound heard by the man sitting in the car will be nearest to
a) 480Hz
b) 510Hz
c) 540Hz
d) 570Hz

View Answer

Answer: c [Reason:] After reflection from the wall, the sound moves towards observer in the car, γ=(v+v0)/(v-vs)×γ=(340+20)/(340-20)×480=540Hz

5. A racing car moving towards a cliff sound its horn. The driver observes that the sound reflected from the cliff has a pitch one octave higher than the actual sound of the horn. If v is the velocity of sound, the velocity of the car is
a) v/√2
b) v/2
c) v/3
d) v/4

View Answer

Answer: c [Reason:] γ/γ=(v+vs)/(v-vs)=2 v+vs=2v-2vs 3vs=v or vs=v/3

6. If a particle travelling with a speed of 0.9 of the speed of sound and is emitting radiations of frequency if 1kHz and moving towards the observer, what is the apparent frequency?
a) 1.1 kHz
b) 0.8 kHz
c) 0.4 kHz
d) 10 kHz

View Answer

Answer: d [Reason:] γ=v/(v-vs)×γ =v/(v-0.9v)×1kHz=10kHz

7. Two trains, each moving with a velocity of 30m/s, cross each other. One of the trains gives a whistle whose frequency is 600Hz. If the speed of sound is 330m/s, the apparent frequency for passengers sitting in the other train before crossing would be
a) 600Hz
b) 630Hz
c) 930Hz
d) 720Hz

View Answer

Answer: d [Reason:] γ=v/(v-vs)×γ =(330—30)/(330-30)×600 360/300×600=720Hz

8. The phenomenon by which stars recede from each other is explained by
a) Black hole theory
b) Neutron star theory
c) White dwarf
d) Red shift

View Answer

Answer: d [Reason:] Red shift confirms that stars are continuously receding away from each other.

9. Speed of recession of galaxy is proportional to its distance
a) Directly
b) Inversely
c) Exponentially
d) Linearly

View Answer

Answer: a [Reason:] According to Hubble’s law, the speed of recession (v) of a galaxy is directly proportional to its distance (r) from us. Where H is Hubble’s constant.

10. The loudness and pitch of a sound note depends on
a) Intensity and frequency
b) Frequency and number of harmonics
c) Intensity and velocity
d) Frequency and velocity

View Answer

Answer: a [Reason:] Loudness depends on intensity while pitch depends on frequency of sound

Set 3

1. A metal plate 5cm×5cm rest on a layer of castor oil 1mm thick whose coefficient of viscosity is 1.55Nsm(-2). Find the horizontal force required to move the plate with a speed of 2 cms(-1).
a) 0.775N
b) 0.0577N
c) 0.0775N
d) 0.577N

View Answer

Answer: c [Reason:] F=ȠA dv/dx F=1.55×25×10-4×(2×10-2)/(1×10-3 )=0.0775N

2. At what speed will the velocity head of stream of water be 40 cm?
a) 2.80cms-1
b) 280 cms-1
c) 28 cms-1
d) 0.280 cms-1

View Answer

Answer: b [Reason:] h=v2/2g v=√2gh=√(2×980×40)=280cms-1

3. It is easier to cut an apple with a blunt knife than a sharp knife. True or false?
a) True
b) False

View Answer

Answer: b [Reason:] The area of a sharp edge is much less than the area of a blunt edge. For the same total force, the effective force per unit area is more for the sharp edge than the blunt one. Hence a sharp knife cuts easily than a blunt knife.

4. It is easier to swim in sea water than in river water. True or false?
a) True
b) False

View Answer

Answer: a [Reason:] The sea water has many salts dissolved in it. So the density of sea water is greater than that of river water. Consequently, the sea water exerts greater upthrust on the swimmer than the river water. Hence it is easier to swim in sea water than in river water.

5. If there were no gravity, which of the following will not be there for a fluid?
a) Viscosity
b) Surface tension
c) Pressure
d) Archimedes’ upward thrust

View Answer

Answer: d [Reason:] Archimedes’ upward thrust will be absent for a fluid, if there were no gravity.

6. Motion of a liquid in a tube is best described by
a) Bernoulli theorem
b) Poiseuille’s equation
c) Stoke’s law
d) Archimedes’ principle

View Answer

Answer: b [Reason:] Poiseuille’s formula gives the volume of a liquid flowing out per second through a horizontal capillary tube of length l, radius r, under a pressure difference p applied across its ends. Q=V/t=(πpr4)/8Ƞl

7. Critical velocity of the liquid
a) Decrease when radius decreases
b) Increases when radius increases
c) Decreased when density increases
d) Increases when density increases

View Answer

Answer: c [Reason:] vc=(Re Ƞ)/pD Critically velocity decreases when density ρ increases or diameter D increases.

8. A steel ball is dropped in oil, then
a) The ball attains constant velocity after sometime
b) The ball stops
c) The speed of ball will keep on increasing
d) The speed of the ball will decrease

View Answer

Answer: a [Reason:] The ball attains constant velocity after falling through some distance in oil when the weight of ball gets balanced by upthrust and the upward viscous force.

9. An aeroplane gets its upward lift due to a phenomenon described by the
a) Archimedes’ principle
b) Bernoulli’s principle
c) Buoyancy principle
d) Pascal law

View Answer

Answer: b [Reason:] An aeroplane gets dynamic upward lift in accordance with Bernoulli’s principle.

10. The rate of flow of liquid through an orifice of a tank does not depend upon
a) The size of orifice
b) Density of liquid
c) The height of fluid column
d) Acceleration due to gravity

View Answer

Answer: d [Reason:] The rate of flow of liquid through an orifice depends on size of orifice, atomising surface area, liquid characteristic. It does not depend on acceleration due to gravity.

11. The velocity of efflux of a liquid through an orifice in the bottom of the tank does not depend upon
a) Size of orifice
b) Height of liquid
c) Acceleration due to gravity
d) Quantity

View Answer

Answer: a [Reason:] Velocity of efflux, v=√2gh Clearly, it does not depend on the size of the orifice.

12. Assertion: Smaller drops of liquid resist deforming forces better than the larger drops [Reason:] Excess pressure inside a drop is directly proportional to its surface area
a) Both assertion and reason are true and reason is the correct explanation of the assertion
b) Both assertion and reason are true but reason is not the correct explanation of the assertion
c) Assertion is true but reason is false
d) Assertion and reason is false

View Answer

Answer: c [Reason:] The assertion is true but the reason is false. The excess pressure inside a liquid drop, p=2σ/R The excess pressure is large in a small drop due to which it can resist the deforming forces.

13. A body of mass 15kg is dropped into the water. If the apparent weight of the body is 107N, then the applied thrust will be
a) 40 N
b) 80 N
c) 60 N
d) 100 N

View Answer

Answer: a [Reason:] Apparent weight = Weight – Upthrust Therefore, Upthrust = Weight – apparent weight Upthrust = 15×9.8 – 107 = 147 – 107 = 40 N

Set 4

1. If the stress is S and the Young’s modulus is Y of material of a wire, the energy stored in the wire per unit volume is
a) 2Y/S
b) S/2Y
c) 2S2 Y
d) S2/ 2Y

View Answer

Answer: d [Reason:] Elastic potential energy stored per unit volume, u=1/2×Stress×Strain=1/2×Stress×Stress/Y=S2/2Y

2. Two wires have the same material and have the same volume. However wire 1 had cross sectional area A and wire 2 has cross sectional area 3A. If the length of wire 1 increases by ∆x on applying force F, how much force is needed to stretch wire 2 by the same amount?
a) F
b) 4F
c) 6F
d) 9F

View Answer

Answer: d [Reason:] Y=F/A l/∆l=F/A2 Al/∆x=FV/(A2 ∆x) F=Y∆x/V A2 FαA2 F=(3A)2 F/F=9 F=9F

3. Amorphous solids are true solids. True or false?
a) True
b) False

View Answer

Answer: b [Reason:] Amorphous solids have disordered arrangement of atoms or molecules. The molecules of liquid are free to move but the molecules of an amorphous solid are almost fixed at their positions. That is why, we say amorphous solids are super-cooled liquids of high velocity.

4. An example for a perfectly plastic body is
a) Quartz
b) Crystal
c) Putty
d) Rubber

View Answer

Answer: c [Reason:] If, on removal of deforming force, a body does not regain its original configuration even a little, then it is said to be a perfectly plastic body. Thus putty is a perfectly plastic body.

5. No material is perfectly elastic. True or false?
a) True
b) False

View Answer

Answer: a [Reason:] All materials undergo a change in their original state, howsoever small it may be, after the removal of deforming force. Hence, there is no such material which is perfectly elastic.

6. A given quantity if an ideal gas is at pressure P and absolute temperature T. What is the isothermal bulk modulus of the gas?
a) 2P/3
b) P
c) 3P/2
d) 2P

View Answer

Answer: b [Reason:] Isothermal bulk modulus of a gas = Pressure of the gas = P

7. A wire fixed at the upper end stretches by length l by applying a force F. What is the work done in stretching?
a) F/2l
b) Fl
c) 2Fl
d) Fl/2

View Answer

Answer: d [Reason:] W = 1/2Stretching force×increase in length W = 1/2 Fl

8. The term liquid crystal refers to a state that is intermediate between
a) Crystalline solid and amorphous liquid
b) Crystalline solid and vapour
c) Amorphous liquid and its vapour
d) A crystal immersed in a liquid

View Answer

Answer: a [Reason:] Liquid crystal is a state intermediate between crystalline solid and amorphous liquid.

9. Which of the following have well defined geometrical external shapes?
a) Amorphous solids
b) Liquids
c) Gases
d) Crystalline solids

View Answer

Answer: d [Reason:] Crystalline solids have well defined geometrical external shapes because the atoms and molecules are arranged in a definite geometrical repeating manner throughout the body of the crystal.

10. A body of weight mg is hanging on a string which extends in length by l. The work done in extending the string is
a) mgl
b) mgl/2
c) 2mgl
d) 0

View Answer

Explanation: W=Average force × extension W=1/2 F×l=1/2 mg×l=mgl/2

Set 5

1. Which is different from others by units?
a) Phase difference
b) Mechanical equivalent
c) Loudness of sound
d) Poisson’s ratio

View Answer

Answer: d [Reason:] Of all the given quantities, Poisson’s ratio has no units.

2. The waves, in which the particles of the medium vibrate in a direction perpendicular to the direction of wave motion, is known as
a) Transverse waves
b) Longitudinal waves
c) Propagated waves
d) Magnetic waves

View Answer

Answer: a [Reason:] In a transverse waves, particles of the medium vibrate in a direction perpendicular of the wave

3. The waves produced by a motor boat sailing in water are
a) Transverse
b) Longitudinal
c) Longitudinal and transverse
d) Stationary

View Answer

Answer: c [Reason:] Transverse waves are generated on the water surface. Inside water longitudinal waves longitudinal waves are produced due to vibrations of the rudder.

4. For a wave propagating in a medium, identify the property that is independent of the others.
a) Velocity
b) Wavelengths
c) Frequency
d) All these depend on each other

View Answer

Answer: c [Reason:] Wave velocity=frequency×wavelength Frequency remains unchanged while velocity and wavelength and interdependent.

5. A boat at anchor is rocked by waves, whose crests are 100m apart and velocity is 25m/s. The boat bounces up once in every
a) 2500s
b) 75s
c) 4s
d) 0.25s

View Answer

Answer: c [Reason:] ʎ=100m, v=25m/s T=ʎ/v=100/25=4s

6. A transverse wave passes through a string with the equation
y=10sinπ(0.02x-2t)
Where x is in metres and t in seconds. The maximum velocity of the particles in wave motion is
a) 63m/s
b) 78m/s
c) 100m/s
d) 121m/s

View Answer

Answer: a [Reason:] y=10sinπ(0.02x-2t) u=dy/dt=-20πcosπ(0.02x-2t) umax=20π=63m/s

7. If equation of a sound wave is
y=0.0015sin⁡(62.8x+314t)
Then its wavelength will be
a) 0.1unit
b) 0.2units
c) 0.3unit
d) 2unit

View Answer

Answer: a [Reason:] y=0.0015sin⁡(62.8x+314t) y=asin⁡(2π/ʎ x+2π/T t) 2π/ʎ=62.8 ʎ= (2×3.14)/62.8=0.1unit

8. The plane wave is described by the equation
y=3cos⁡(x/4-10t-π/2),
Where c is in meters and t in seconds. The maximum velocity of the particles of the medium due to this is
a) 30m/s
b) 3π/2 m/s
c) ¾ m/s
d) 40m/s

View Answer

Answer: a [Reason:] y=3cos⁡(x/4-10t-π/2) u=dy/dt=30sin⁡(x/4-10t-π/2) umax=30m/s

9. The equation of wave is given by
y=10sin⁡(2πt/30+α)
If the displacement is 5cm at t=0, then the total phase at t=7.5s will be
a) π/3rad
b) π/2rad
c) 2π/5rad
d) 2π/3rad

View Answer

Answer: d [Reason:] y=10sin⁡(2πt/30+α) At t=0, 5=10sinα or sin α=1/2 α=π/6 Total phase at t=7.5s, φ=(2π×7.5)/300+π/6=π/2+π/6=2π/3

10. If two sound waves having a phase difference of 60°, then they will have a path difference of
a) ʎ/6
b) ʎ/3
c) ʎ
d) 3ʎ

View Answer

Answer: a [Reason:] ∆φ=60°=π/3 ∆x=ʎ/2π×∆φ=ʎ/2π×π/3=ʎ/6