Dashboard / My courses / 1152_PHY F111 / Quiz 1 / Quiz 1
Started on Wednesday, 20 April 2022, 5:10 PM
State Finished
Completed on Wednesday, 20 April 2022, 5:50 PM
Time taken 39 mins 35 secs
Grade 20.00 out of 40.00 (50%)
Question 1
Correct
Mark 4.00 out of 4.00
The vibrational frequency of a stretched string of a musical instrument is 300Hz. The energy of oscillation of the string falls to
1/3rd of its initial value in 1.4 seconds.
Find the quality factor of the vibrating string. The answer should be expressed in two decimal places.
Answer: 2402.06 !
The correct answer is: 2402.07
Question 2
Incorrect
Mark 0.00 out of 6.00
Two radio stations broadcast their programmes at the same amplitude A, and at slightly different frequencies ω1
and ω2 respectively, where ω2 – ω1 = 2π x 9 Hz. A detector receives the signals from the two stations simultaneously. It can only
detect signals of intensity >= 2A2 that is amplitude ±√2 ‾ A . Find the time (in seconds) for which the detector remains idle
(does not detect any signal) in each cycle of the intensity of the signal. Note that a cycle of intensity refers to the time interval
between two consecutive maxima (or minima) of intensity, as intensity cannot have any negative value.
Answer upto three decimal places after rounding off.
Answer: 0.111 "
The correct answer is: 0.056
Question 3
Incorrect
Mark 0.00 out of 6.00
The energy of recoil of a rocket launcher of mass m = 4500 kg is absorbed in a recoil spring. When the rocket is launched, the
launcher recoils 8 m with an initial speed of 10 ms−1 . At the end of the recoil, a damping dashpot is arranged in such a way that
the launcher returns to the firing position without any oscillation (critical damping). Find the dashpot’s damping constant γ in
s−1 .
s .
Write your answer upto two decimal places after rounding off.
Answer: 7.57 "
The correct answer is: 2.50
Question 4
Correct
Mark 4.00 out of 4.00
A mass of m = 0.8 kg , connected with
horizontal spring with spring constant k = 180 Nm−1 ,
performs simple harmonic motion. At time t=0 the mass is
observed to be 0.04 m further from the equilibrium position
and is moving away from the equilibrium position with a
velocity of 0.5 ms−1 .
Let the displacement of the mass be x = Acos(ωt + ϕ) .
(a)
ω=
15
!
(b)
A=
0.052
Question 5
Correct
Mark 4.00 out of 4.00
An electron in an excited atom behaves like a
damped harmonic oscillator when the atom radiates light.
The lifetime of an excited atomic state is 10−8 s
and the wavelength of the emitted light is 500 nm (nano meter).
[Note: Quality factor = Q ]
10−7 Q =
3.77
Question 6
Correct
Mark 4.00 out of 4.00
A forced damped harmonic oscillator ,
driven by a force F0 cosωt ,
vibrates with an steady state amplitude A(ω) .
The steady state amplitude A(ω) is maximum at ω res .
[ Note: natural frequency =ω 0 and Quality factor Q = 10 ]
ωres
=
2ω0
0.5
Question 7
Correct
Mark 4.00 out of 4.00
The equation of a forced damped oscillator is :
ẍ + 10ẋ + (2π ∗ 600)2 x = 1000cos(2π ∗ 700)t
.
Considering the damping to be low but non-zero, choose which of the following statements are correct. (You have to choose all
the correct options if multiple options are correct).
Select one or more:
At 0.1 s, the frequency is approximately 700 Hz.
At 10 s, the frequency is approximately 700 Hz. !
At 0.1 s, the amplitude is constant in time.
At 10 s, the frequency is approximately 600 Hz.
At 10 s, the amplitude is constant in time. !
Your answer is correct.
The correct answers are: At 10 s, the amplitude is constant in time., At 10 s, the frequency is approximately 700 Hz.
Question 8
Incorrect
Mark 0.00 out of 4.00
Consider the power resonance graph of a Forced Damped Oscillation as shown in the figure. What fraction(in percentage) of the
initial energy is lost in one cycle ?
Express your answer as a multiple of π. If your answer is 50π, then write only 50 in the answer.
Answer: 1.91 "
The correct answer is: 12
Question 9
Incorrect
Mark 0.00 out of 4.00
From the figure given below what is the ratio of horizontal frequency and vertical frequency. If your answer is decimal express it
in one decimal point. If it is an integer then write the integer value.
Answer: 1 "
The correct answer is: 0.7
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