Engineering Questions with Answers - Multiple Choice Questions
Stationary Waves
1 - Question
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
Explanation: γ‘=v/(v-vs)×γ=350/(350-25)×1000Hz
=1077Hz.
2 - Question
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
Explanation: As γ‘=v/(v-vs)×γ
vs=36km/h=10m/s
ʎ‘=(v-vs)/v×ʎ=(330-10)/330×1=32/33 m.
3 - Question
The source of sound generating of a 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
Explanation: γ‘=v/(v-vs)×γ
=v/(v-0.5γ)×3kHz=6kHz.
4 - Question
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
Explanation: 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 - Question
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
Explanation: γ‘/γ=(v+vs)/(v-vs)=2
v+vs=2v-2vs
3vs=v or vs=v/3.
6 - Question
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
Explanation: γ‘=v/(v-vs)×γ
=v/(v-0.9v)×1kHz=10kHz.
7 - Question
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
Explanation: γ‘=v/(v-vs)×γ
=(330+30)/(330-30)×600
360/300×600=720Hz.
8 - Question
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
Explanation: Red shift confirms that stars are continuously receding away from each other.
9 - Question
Speed of recession of a galaxy is proportional to its distance __________
a) Directly
b) Inversely
c) Exponentially
d) Linearly
View Answer
Answer: a
Explanation: 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 - Question
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
Explanation: Loudness depends on intensity while pitch depends on the frequency of sound.