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Multiple choice question for engineering

Set 1

1. How are sound waves with frequency of 20Hz to 20,000Hz termed?
a) Inaudible sounds
b) Infrasonics
c) Ultrasonics
d) Audible sound

View Answer

Answer: d [Reason:] Sound waves below the frequency of 20Hz are infrasonics. Sound waves above 20,000Hz are ultrasonics. Both are inaudible. Sound waves between 20Hz to 20,000Hz are audible sounds.

2. Sound of mosquito produces high pitch than the sound of lion. True or false?
a) True
b) False

View Answer

Answer: a [Reason:] Pitch depends directly on the frequency of incident sound waves. Though pitch is directly related to frequency, they are not the same. In general, frequency is physical quantity whereas the pitch is physiological quantity.

3. What is the quantity that helps us distinguish a particular voice of a singer from the voice of many singers?
a) Timbre
b) Pitch
c) Intensity
d) Music

View Answer

Answer: a [Reason:] The timbre or quality of sound is one which helps us to distinguish between musical notes emitted by different musical instruments or voices, even though they have the same pitch and loudness.

4. Sensitivity increases with decrease in intensity. True or false?
a) True
b) False

View Answer

Answer: b [Reason:] L = k log I Differentiating the above equation, dL/dI = k/I Therefore sensitivity decreases with increase in intensity.

5. What happens if the reverberation time is too large?
a) The sound becomes inaudible
b) Echoes are produced
c) Frequency becomes high
d) The sound becomes infrasonic

View Answer

Answer: b [Reason:] Reverberation is the time taken for the sound to fall below the minimum audibility measured from the instant when the source stopped sounding. Therefore if the reverberation time becomes too large it produces echo.

6. What will happen when sound is focussed to a particular area?
a) Echoes are produced
b) Sound becomes inaudible
c) Interference occurs
d) Frequency of sound becomes high

View Answer

Answer: c [Reason:] When sound waves are produced in a hall, it reaches the observer directly as well as after reflections from walls, floors, ceilings etc. Thus when sound is focussed to a particular area it is possible that interference is produced between the waves, which in turn affect the originality of the sound.

7. Sound produced from equally spaced steps in a stair case at regular intervals is due to which effect?
a) Reverberation effect
b) Noise effect
c) Absorption effect
d) Echelon effect

View Answer

Answer: d [Reason:] If there is a regular repetition of the original sound to the observer then the effect is called Echelon effect. Sound produced by equally spaced steps in a stairs at regular intervals produce echelon effect.

8. What happens when window panel sections of the wooden portions are thrown into vibrations to produce new sounds?
a) Vibrations are produced
b) Resonance occurs
c) Echoes are produced
d) Absorption occurs

View Answer

Answer: b [Reason:] Resonance occurs when a new sound not of frequency matches with standard audio frequency. When window panel sections, of the wooden portions are thrown into vibrations to produce new sounds it results in interference between original sound and created sound. This will create disturbance to the audience.

9. A cinema theatre has a volume of 750m2. What should be the total absorption in the theatre if the reverberation time of 1.5seconds is to be maintained?
a) 835 open window units
b) 1125 open window units
c) 500 open window units
d) 750 open window units

View Answer

Answer: a [Reason:] Reverberation time = 0.167/Σas Total absorption Σas = 0.167V/T Total absorption = 835 open window units

Set 2

1. The quantity which has only magnitude is called
a) A scalar quantity
b) A vector quantity
c) A chemical quantity
d) A magnitude quantity

View Answer

Answer: a [Reason:] A quantity which has only magnitude and no direction is called scalar quantity. Example: mass

2. Force is a vector quantity. True or false?
a) True
b) False

View Answer

Answer: a [Reason:] Force has both magnitude and direction. A quantity which has both magnitude and direction is called a vector quantity. Therefore, force is a vector quantity.

3. A polar vector is one which
a) Gives the position of an object
b) Tells how much and in which direction an object has changed its position
c) Represents rotational effect
d) Has a starting point of application

View Answer

Answer: d [Reason:] The vector which has a starting point or a point of application is called polar vector. Velocity maybe regarded as polar vector.

4. Which of the following acts in accordance with right hand screw rule?
a) Polar vector
b) Axial vector
c) Displacement vector
d) Position vector

View Answer

Answer: b [Reason:] The vectors which represent rotational effect and act along the axis of rotation in accordance with right hand screw rule are called axial vector. Axial vector will have its direction along its axis of rotation depending on its anticlockwise or clockwise rotational effect.

5. What is the magnitude of a unit vector?
a) It has no magnitude
b) Zero
c) Constant but not zero
d) Unity

View Answer

Answer: d [Reason:] The magnitude of a unit vector is unity. It just gives the direction of a vector. A unit vector has no units or dimensions.

6. Which have the following has zero magnitude?
a) Fixed vector
b) Zero vector
c) Modulus of a vector
d) Unit vector

View Answer

Answer: b [Reason:] A zero or null vector is a vector that has zero magnitude and an arbitrary direction. The velocity vector of a stationary object is a zero vector.

7. Flying a bird is an example of
a) Collinear vector
b) Multiplication of vector
c) Addition of vector
d) Composition of vector

View Answer

Answer: d [Reason:] When a bird flies, it pushes the air with force in the downward direction with its wings. In accordance with Newton’s law of motion, the air exerts equal and opposite reaction. According to the parallelogram law, the resultant of the reaction acts on the birds in the upward direction and helps the bird to fly upwards.

8. Two forces whose magnitudes are in ratio of 3:5 give a resultant of 35N. If the angle of inclination is 60°, calculate the magnitude of each force.
a) 15N and35N
b) 15N and 25N
c) 10N and 15N
d) 20N and 5N

View Answer

Answer: b [Reason:] P = 3x and Q = 5x R = 35N θ = 120° R = √(P2+ R2+ 2PQcosθ) 35 = 7x or x = 35/7 = 5 P = 15N Q = 25N

9. Walking of a man is an example of
a) Resolution of forces
b) Addition of vectors
c) Subtraction of vectors
d) Multiplication of vectors

View Answer

Answer: a [Reason:] While walking, a person presses the ground with his feet slightly slanted in the backward direction. The ground exerts upon him an equal and opposite reaction. Its horizontal component enables the person to move forward while the vertical component balances this weight.

Set 3

1. A flywheel has a mass of 25kg has a radius of 0.2m. What force should be applied tangentially to the rim of the flywheel so that it acquires an angular acceleration of 2rad/s2?
a) 2N
b) 5N
c) 3N
d) 1N

View Answer

Answer: b [Reason:] M = 25kg, R = 0.2m, α = 2rad/s2 Moment of inertia of the flywheel about its axis, I = 1/2 MR2=1/2×25×0.22=0.5kgm2 As torque, τ = F×R=I×α Therefore, Force F = Iα/R=(0.5×2)/0.2=5N

2. A torque of 10Nm is applied to a flywheel of mass 1kg and radius of gyration 50cm. What is the resulting angular acceleration?
a) 4 rad/s2
b) 2 rad/s2
c) 5 rad/s2
d) 6 rad/s2

View Answer

Answer: a [Reason:] τ=10Nm, M = 10kg, K = 0.50m As τ=I×α= MK2 α α=τ/(MK2 )=10/(10×0.502 )=4 rad/s2

3. The angular momentum of a body is 3.14 is and its rate of revolution is 10 cycles per second. Calculate the moment of inertia of the body about the axis of rotation.
a) 5 kgm2
b) 0
c) 31.4 kgm2
d) 0.5 kgm2

View Answer

Answer: d [Reason:] L = 3.14 Js v = 10 rps ω=2πv=2×3.14×10/rad As L = Iω I = L/ω = 3.14/(2×3.14×10)=0.5kgm2

4. The angular velocity of a planet revolving in an elliptical orbit around the sun increases, when it comes closer to the sun. This is due to
a) Conservation of momentum
b) Newton’s second law of motion
c) Conservation of angular momentum
d) Law of angular velocity

View Answer

Answer: c [Reason:] The angular velocity of a planet revolving in an elliptic orbit around the sun increases when it comes closer to the sun increases, when it comes closer to the sun because its moment of inertia about the axis through the sun decreases. When it goes far away from the sun, its moment of inertia decreases so as to conserve angular momentum.

5. An ice skater or a ballet dancer can decrease her angular velocity by folding her arms and bringing the stretched leg close to the other leg. True or false?
a) True
b) False

View Answer

Answer: b [Reason:] An ice skater can increase her angular velocity by folding her arm and bringing the leg closer to the other. When she stretches her hand outward, her moment of inertia increases and hence angular speed decreases to conserve angular momentum. When she fold her hands and brings the stretched legs close to the other leg, her moment of inertia decreases and hence her angular speed increases.

6. The centre of mass of a body should lie inside the body. True or false?
a) True
b) False

View Answer

Answer: b [Reason:] The centre of mass of a body need not necessarily lie inside the body. The centre of mass of a ring lies in its hollow portion.

7. In a hand driven grinding machine, handle is put
a) Perpendicular to the stone
b) Near the circumference of the stone
c) A few distances above the stone
d) As far away from the stone

View Answer

Answer: b [Reason:] For a given force, torque can be increased if the perpendicular distance of the point of application of the force from the axis of rotation is increased. Hence the handle put near the circumference produces maximum torque.

8. A faulty balance with unequal arms has its beam horizontal. The weights of the two pans is
a) Equal
b) Unequal
c) Uncertain
d) Very large

View Answer

Answer: b [Reason:] They are of unequal mass. Their masses are in the inverse ratio of the arms of the balance.

9. Which part of the ship is made heavy?
a) The whole ship should be light in weight
b) The top part
c) The bottom part
d) The sides

View Answer

Answer: c [Reason:] The bottom of the ship is made heavy so that the centre of gravity remains low. This ensures the stability of its equilibrium.

10. Standing is not allowed in double decker bus. True or false?
a) True
b) False

View Answer

Answer: a [Reason:] When the passengers stand in the upper deck, the centre of gravity of the loaded bus is raised this makes it less stable.

Set 4

1. The bob of the pendulum moves faster at the lowest position for a larger amplitude. True or false?
a) True
b) False

View Answer

Answer: a [Reason:] We know that the velocity of a simple pendulum is maximum at the lowest position and is given by vmax=ωA That is for larges amplitude, the bob of the pendulum would move faster.

2. The total energy of a particle executing simple harmonic motion is
a) ∝x
b) ∝x2
c) Independent of x
d) ∝√x

View Answer

Answer: c [Reason:] E=2π2mv2A2 Clearly, the total energy is independent of displacement x

3. A body executes simple harmonic motion. The potential energy, the kinetic energy and total energy are measured as function of displacement x. Which of the following statements is true?
a) Kinetic energy is maximum, when x =0
b) Total energy is zero, when x = 0
c) Kinetic energy is maximum, when x is maximum
d) Potential energy is maximum, when x = 0

View Answer

Answer: a [Reason:] The kinetic energy of a simple harmonic oscillator is maximum when x = 0

4. Two simple motions are represented by
y1=5(sin2πt+√3 cos2πt)
y2=5sin⁡(2πt+π/4)
The ratio of the amplitude of two simple harmonic motions is
a) 1:1
b) 1:2
c) 2:1
d) 1:√3

View Answer

Answer: c [Reason:] y1=5×2(sin2πtcos(π/3)+sin⁡(π/3)cos2πt) y1=10sin⁡(2πt+(π/3) ) y2=5sin⁡(2πt+(π/4) ) A1/A2 =10/5=2:1

5. The ratio of frequencies of two pendulums is 2:3 then their lengths are in ratio
a) √(2/3)
b) √(3/2)
c) 4/9
d) 9/4

View Answer

Answer: d [Reason:] v1/v2 =√(l2/l1 ) l1/l2 =((v2)2)/((v1)2 )=9/4

6. For a particle executing simple harmonic motion, which of the following statements is not correct?
a) Total energy is always directed towards a fixed point
b) Restoring force is always directed towards a fixed point
c) Restoring force is maximum at the extreme positions
d) Acceleration of the particle is maximum at the equilibrium position

View Answer

Answer: d [Reason:] At the equilibrium position, the velocity of a particle in dimple harmonic motion is maximum and consequently its acceleration is minimum.

7. If a spring of mass 30kg has a spring constant of 15N/m, then its time period is
a) 2πs
b) 2√2 πs
c) 2√2π s
d) 2√2 s

View Answer

Answer: b [Reason:] T=2π√(m/k) T=2π√(30/15)=2π√2 s

8. Statement: Water in a U-tube executes simple harmonic motion. The time period for mercury filled up to the same height in the U-tube be greater than that in case of water [Reason:] The amplitude of an oscillating pendulum goes on increasing
a) Both statement and reason are true and reason is the correct explanation of the statement
b) Both statement and reason are true but reason is not the correct explanation of the statement
c) Statement is true, but reason is false
d) Statement and reason are false

View Answer

Answer: d [Reason:] Both the statement and reason are false. Period of oscillation of a liquid in a U-tube is independent of the density of the liquid. The amplitude is the oscillating pendulum decreases due to air friction.

9. A spring (spring constant = k) is cut into 4 equal parts and two parts are connected in parallel. What is the effective spring constant?
a) 4k
b) 16k
c) 8k
d) 6k

View Answer

Answer: c [Reason:] Spring constant of each one-fourth part = 4k When two parts are connected in parallel, kp=4k+4k=8k

10. The periodic time of a body executing simple harmonic motion is 4s. After how much interval from time t=0, its displacement will be half of its amplitude?
a) ½ s
b) 1/3 s
c) ¼ s
d) 1/6 s

View Answer

Answer: b [Reason:] As seen in the above problem, t=1t/12=4/12=1/3 s

Set 5

1. Statement: Ocean waves hitting a beach are always found to be nearly normal to the shore [Reason:] Once waves hitting a beach are assumed to be plane waves
a) Both statement and reason are true and reason is the correct explanation of the statement
b) Both statement and reason are true but reason is not the correct explanation of the statement
c) Statement is true but reason is false
d) Both statement and reason are false

View Answer

Answer: a [Reason:] Both the statement and reason are true. Once waves are transverse in nature, they hit the shore normally. As these waves spread out, their radius of curvature becomes so large that they may be considered as plane waves.

2. Statement: When a beetle moves along the sand within a few tens of centimetres of a sand scorpion, the scorpion immediately turns towards the beetle and dashes towards it [Reason:] When a beetle disturbs the sand, it sends pulses is longitudinal, while the other set in transverse
a) Both statement and reason are true and reason is the correct explanation of the statement
b) Both statement and reason are true but reason is not the correct explanation of the statement
c) Statement is true but reason is false
d) Both statement and reason are false

View Answer

Answer: a [Reason:] Both the statement and reason are true. A beetle’s motion sends fast longitudinal and slower transverse waves along sand’s surface. The sand scorpion intercepts the longitudinal waves first and senses the direction of the beetle by noting which are of the eight legs of the scorpion is disturbed first by the pulses. Then the scorpion dashes towards the beetle to catch it

3. Statement: When two vibration tuning forks having frequencies 256Hz and 512Hz are held near each other, beats cannot be heard [Reason:] The principle of superposition is valid if the frequencies of the oscillators are nearly equal
a) Both statement and reason are true and reason is the correct explanation of the statement
b) Both statement and reason are true but reason is not the correct explanation of the statement
c) Statement is true but reason is false
d) Both statement and reason are false

View Answer

Answer: c [Reason:] The statement is true but the reason is false. The beats can be heard only if the two sounds do not exceed 10Hz.

4. A wave of frequency 100Hz travels along a string towards its fixed end. When this wave travels back, after reflection, a node is formed at a distance of 10cm from the fixed end. The speed of the wave (incident and reflected) is
a) 20m/s
b) 40m/s
c) 5m/s
d) 10m/s

View Answer

Answer: a [Reason:] Since a node is formed at the fixed end, so ʎ/2=10cm or ʎ=20cm γ=100Hz v=ʎγ=100×0.20=20m/s

5. A vehicle, with a horn of frequency n is moving with a velocity of 30m/s in a direction perpendicular to the straight line joining the observer and the vehicle. The observer perceives the sound to have a frequency n+n1. Then (if the sound velocity in air is 300m/s)
a) n1=0.1n
b) n1=0
c) n1=10n
d) n1=-0.1n

View Answer

Answer: b [Reason:] As the vehicle moves in direction perpendicular to the line joining the observer and he vehicle, the component of the velocity along this direction zero. There is no Doppler effect and the frequency of sound remains unchanged.

6. Lights can travel in vacuum but not sound, because
a) Speed of sound is very slow than light
b) Light waves are electromagnetic in nature
c) Sound waves are electromagnetic in nature
d) Light waves are not electromagnetic in nature

View Answer

Answer: a [Reason:] Light can travel in vacuum because light waves are electromagnetic in nature

7. Velocity of sound in air is
a) Faster in dry air than in moist air
b) Directly proportional to temperature
c) Directly proportional to pressure
d) Slower in dry air than in moist air

View Answer

Answer:b [Reason:] Velocity of sound is proportional to temperature. It is independent of pressure and increase with humidity

8. When sound travels from air to water, which parameter does not change?
a) Wavelength
b) Frequency
c) Velocity
d) Temperature

View Answer

Answer: b [Reason:] Frequency remains unchanged when sound travels from air to water

9. The apparent frequency in Doppler’s effect does not depend upon
a) Speed of the observer
b) Distance between the observer and source
c) Speed of the source
d) Frequency of the source

View Answer

Answer: b [Reason:] Apparent frequency in Doppler’s effect depends on frequency of source, direction and velocity of source and observer. It does not depend on the distance between observer and source.

10. In a sinusoidal wave, the time required for a particular point to move from maximum displacement to zero displacement is 0.107sec. The frequency of wave is
a) 0.73Hz
b) 0.36Hz
c) 1.47Hz
d) 2.94Hz

View Answer

Answer: c [Reason:] Time taken in moving from maximum displacement to zero displacement is T/4=0.170s or T=0.68s Frequency, v=1/T=1/0.67=1.47Hz

11. Wave has simple harmonic motion whose period is 4seconds while another wave which also possesses simple harmonic motion has its period 3sec. If both are combined, then the resultant wave will have the period equal to
a) 4sec
b) 5sec
c) 12sec
d) 3sec

View Answer

Answer: c [Reason:] On superposition of the two waves, beats are produced. Beat frequecny=1/T2 -1/T1 =1/3-1/4=1/12 Time period=12seconds

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