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All questions of Oscillations for NEET Exam

Find the amplitude of the S.H.M whose displacement y in cm is given by equation y= 3sin 157t +4cos157t where t is time in seconds.
  • a)
    20Hz
  • b)
    25Hz
  • c)
    50Hz
  • d)
    40Hz
Correct answer is option 'B'. Can you explain this answer?

When the displacement of a SHM is:
y=a sin wt+ b cos wt
  • Amplitude of the SHM will be:
    A=√a2+b2
Here, a = 3, b = 4
Amplitude, A= √(32+42) = 5 cm
Hence option B is correct.

Two identical spring, each of stiffness k are welded to each other at point P. The other two ends are fixed to the edge of a smooth horizontal tube as shown. A particle of mass m is welded at P. The entire system is horizontal. The period of oscillation of the particle in the direction of x is   
  • a)
  • b)
  • c)
  • d)
Correct answer is option 'D'. Can you explain this answer?

Mohit Rajpoot answered
Let us assume a force dF is applied at P in positive x - direction. This will stretch each spring by dl inducing a spring force dFs in each spring.
Let the static deformation of the system is dx (along the x-direction). The particle is in equilibrium. So,
Using Pythagoras theorem, 
Here y is constant. 
 

A second pendulum is mounted in a space shuttle. Its period of oscillations will decrease when rocket is
  • a)
    moving in geostationary orbit
  • b)
    ascending up with uniform acceleration
  • c)
    descending down with uniform acceleration
  • d)
    moving up with uniform velocity
Correct answer is option 'B'. Can you explain this answer?

Top Rankers answered
 
  • Time Period, T = 2π √(l/g')where,
    l = Length of seconds pendulum 
    g’ = Apparent Gravity
  • For the period of oscillations of Seconds Pendulum to decrease, the Apparent gravity (g’) has to increase because:
  • Hence, Time Period of oscillations of Seconds Pendulum will decrease when the rocket is ascending up with uniform acceleration.

If a simple pendulum oscillates with an amplitude 50 mm and time period 2s, then its maximum velocity is
a)0.15 m/s
b)0.1 m/s
c)0.16 m/s
d)0.8 m/s
Correct answer is option 'A'. Can you explain this answer?

Neha Joshi answered
We know that in a simple harmonic motion the maximum velocity,
Vmax = A⍵
Here A = 50 mm
And ⍵ = 2π / T
= 2π / 2
= π
Hence  Vmax = 50 x 10-3
= 0.15 m/s

What will be the phase difference between bigger pendulum (with time period 5T/4 )and smaller pendulum (with time period T) after one oscillation of bigger pendulum?
  • a)
    π/4
  • b)
    π/2
  • c)
    π/3
  • d)
    π
Correct answer is option 'B'. Can you explain this answer?

Preeti Iyer answered
By the time bigger pendulum completes one vibration, the smaller pendulum would have completed 5/4 vibrations. That is smaller pendulum will be ahead by 1/4 vibration in phase. 1/4 vibration means λ/4 path or π/2 radians.

A frequency of 1Hz corresponds to:
  • a)
    2 vibrations per second
  • b)
    1 vibration per second
  • c)
    10 vibrations per second
  • d)
    a time period of ½ second
Correct answer is option 'B'. Can you explain this answer?

Alok Mehta answered
Frequency used to be measured in cycles per second, but now we use the unit of frequency - the Hertz (abbreviated Hz). One Hertz (1Hz) is equal to one vibration per second. So the weight above is bouncing with a frequency of about 1Hz. The sound wave corresponding to Middle C on a piano is around 256Hz.

What determines the natural frequency of a body?
  • a)
    Position of the body with respect to force applied
  • b)
    Mass and speed of the body
  • c)
    Oscillations in the body
  • d)
    Elastic properties and dimensions of the body
Correct answer is option 'D'. Can you explain this answer?

Lavanya Menon answered
Natural frequency is the frequency at which a body tends to oscillate in the absence of any driving or damping force.
Free vibrations of any elastic body are called natural vibration and happen at a frequency called natural frequency. Natural vibrations are different from forced vibration which happen at frequency of applied force .

The restoring force in a simple harmonic motion is _________ in magnitude when the particle is instantaneously at rest.
  • a)
    zero
  • b)
    maximum
  • c)
    minimum
  • d)
    none of these
Correct answer is option 'B'. Can you explain this answer?

Knowledge Hub answered
The restoring force in a simple harmonic motion is maximum in magnitude when the particle is instantaneously at rest because in SHM object’s tendency is to return to mean position and here particle is instantaneously at rest after that instant restoring force will be max to bring particle to mean position.

If the length of a simple pendulum is increased by 2%, then the time period [1997]
  • a)
    increases by 2%
  • b)
    decreases by 2%
  • c)
    increases by 1%
  • d)
    decreases by 1%
Correct answer is option 'C'. Can you explain this answer?

T=2π√l/g
here we take g=constant..
so T Will b proportional to √l....
for small change in length
ΔT/T=1/2Δl/l
=1/2(2%)
=1% increase (since it is directly proportional)

The amplitude of S.H.M at resonance is _______ in the ideal case of zero damping.
  • a)
    Maximum
  • b)
    Minimum
  • c)
    Zero
  • d)
    Infinite
Correct answer is option 'D'. Can you explain this answer?

Neha Joshi answered
In an ideal environment where there is no resistance to oscillation motion i.e. damping is zero, when we oscillate a system at its resonant frequency since there is no opposition to oscillation, the amplitude will go on increasing and reach infinity.

Two simple pendulums of length 5m and 20m respectively are given small linear displacement in one direction at the same time. They will again be in the phase when the pendulum of shorter length has completed ....... oscillations [1998]
  • a)
    5
  • b)
    1
  • c)
    2
  • d)
    3
Correct answer is option 'C'. Can you explain this answer?

Tejas Chavan answered
Let the pendulums be in phase after t sec of start. Within this time, if the bigger pendulum executes n oscillations, the smaller one will have executed (n + 1) oscillations.
Now, the time of n oscillation =& the time of (n + 1) oscillation
To be in phase
or,      2n = n + 1
or,      n = 1
Hence, the no. of oscillations executed by shorter pendulum = n + 1 = 1 + 1 = 2

A hollow sphere is filled with water. It is hung by a long thread. As the water flows out of a hole at the bottom, the period of oscillation will [1997]
  • a)
    first increase and then decrease
  • b)
    first decrease and then increase
  • c)
    go on increasing
  • d)
    go on decreasing
Correct answer is option 'A'. Can you explain this answer?

Time period of simple pendulum
where l is effective
length. [i.e distance between centre of suspension and centre of gravity of bob]
Initially, centre of gravity is at the centre of sphere. When water leaks the centre of gravity goes down until it is half filled; then it begins to go up and finally it again goes at the centre. That is effective length first increases and then decreases. As  , so time period first increases and then decreases.

In the ideal case of zero damping, the amplitude of simple harmonic motion at resonance is:
  • a)
    zero
  • b)
    infinite
  • c)
    cannot be said
  • d)
    varies from zero to infinite
Correct answer is option 'B'. Can you explain this answer?

Priya Patel answered
In an ideal environment where there is no resistance to oscillatory motion, that is, damping is zero, when we oscillate a system at its resonant frequency, since there is no opposition to oscillation, a very large value of amplitude will be recorded. Forced oscillation is when you apply an external oscillating force.

A simple pendulum has a metal bob, which is negatively charged. If it is allowed to oscillate above a positively charged metallic plate, then its time period will [2001]
  • a)
    increase
  • b)
    decrease
  • c)
    become zero
  • d)
    remain the same
Correct answer is option 'B'. Can you explain this answer?

Gargi Datta answered
Explanation:

When a negatively charged metal bob is placed above a positively charged metallic plate, an electric field is created between them. This electric field exerts a force on the bob, which affects its motion and hence the time period of oscillation.

Electric Field and Force:
The positively charged metallic plate creates an electric field in the region surrounding it. This electric field points towards the plate, from the bob to the plate. Since the bob is negatively charged, it experiences a force in the direction opposite to the electric field.

Effect on Time Period:
The force exerted on the bob due to the electric field affects its motion and hence the time period of oscillation. The time period of a simple pendulum is given by:
T = 2π√(l/g)
where T is the time period, l is the length of the pendulum, and g is the acceleration due to gravity.

As the force due to the electric field opposes the motion of the bob, it effectively increases the effective length of the pendulum. This is because the bob is pushed slightly away from the plate during its oscillation. Therefore, the length of the pendulum increases, leading to an increase in the time period.

Conclusion:
Hence, when a negatively charged metal bob is allowed to oscillate above a positively charged metallic plate, its time period will decrease. Therefore, the correct answer is option 'B' - decrease.

The particle executing simple harmonic motion has a kinetic energy K0 cos2ωt . The maximum values of the potential energy and the total energy are respectively [2007]
  • a)
    K0/2 and K0
  • b)
    K0 and 2K0
  • c)
    K0 and K0
  • d)
    0 and 2K0.
Correct answer is option 'C'. Can you explain this answer?

Meera Singh answered
Given, Kinetic energy=K0cos2ωt
Maximum kinetic energy=K (as ωt=0 and cos ωt=1
Since total energy remains conserved in SHM , hence when potential energy is maximum,Kinetic energy=0  i.e. E is also equal to Umax  i.e.  U max(maximum potential energy) = E(Total energy) = K0

A particle of mass m oscillates along x-axis according to equation x = a sinωt. The nature of the graph between momentum and displacement of the particle is [NEET Kar. 2013]
  • a)
    straight line passing through origin
  • b)
    circle
  • c)
    hyper bola
  • d)
    ellipse
Correct answer is option 'D'. Can you explain this answer?

Tarun Saha answered
(ωt + φ), where a is the amplitude, ω is the angular frequency, t is time, and φ is the phase angle. The displacement of the particle from its equilibrium position at any time t is given by x(t) = a sin(ωt + φ).

The velocity of the particle at any time t is the derivative of the displacement with respect to time, which is given by:

v(t) = aω cos(ωt + φ)

The acceleration of the particle at any time t is the second derivative of the displacement with respect to time, which is given by:

a(t) = -aω^2 sin(ωt + φ)

The negative sign indicates that the acceleration is in the opposite direction to the displacement. This means that when the particle is at its maximum displacement, the acceleration is zero, and when the particle passes through the equilibrium position, the acceleration is maximum.

The period of the motion is the time taken by the particle to complete one full oscillation. It is given by:

T = 2π/ω

The frequency of the motion is the number of oscillations per unit time. It is given by:

f = ω/2π

The maximum velocity of the particle is given by:

v_max = aω

The maximum acceleration of the particle is given by:

a_max = aω^2

The energy of the particle is the sum of its kinetic and potential energies. At any time t, the total energy of the particle is given by:

E(t) = (1/2)mv^2 + (1/2)kx^2

where k is the spring constant. The energy is constant throughout the motion, and is equal to the total energy at any other time.

The phenomenon of increase in amplitude when the driving force is close to the natural frequency of the oscillator is known as
  • a)
    Accelerated Amplitude
  • b)
    Epoch
  • c)
    Resonance
  • d)
    Dampening
Correct answer is option 'C'. Can you explain this answer?

Priya Patel answered
The phenomenon of increase in amplitude when the driving force is close to the natural frequency of the oscillator is known as. The phenomenon of increase in amplitude when the driving force is close to the natural frequency of the oscillator is known as resonance.

Masses MA and MB hanging from the ends of strings of lengths LA and LB are executing simple harmonic motions. If their frequencies are fA = 2fB, then [2000]
  • a)
    LA = 2LB and MA = MB/2
  • b)
    LA = 4LB regardless of masses
  • c)
    LA = LB/4 regardless of masses
  • d)
    LA = 2LB and MA = 2MB
Correct answer is option 'C'. Can you explain this answer?

To understand why the correct answer is option 'C', let's break down the given information and analyze the relationship between the frequencies and lengths of the strings.

Given:
- Masses MA and MB are hanging from strings of lengths LA and LB, respectively.
- The masses are executing simple harmonic motions.
- The frequency of MA, fA, is twice the frequency of MB, fB.

Frequency of Simple Harmonic Motion:
The frequency of an object executing simple harmonic motion is given by the formula:

f = 1/2π * √(k/m)

where f is the frequency, k is the spring constant, and m is the mass of the object.

Analyzing the Given Information:
1. Frequency Relationship:
Since fA = 2fB, we can write the equation as:

1/2π * √(kA/MA) = 2 * (1/2π * √(kB/MB))

Simplifying this equation, we get:

√(kA/MA) = 2 * √(kB/MB)

Squaring both sides of the equation, we have:

kA/MA = 4 * (kB/MB)

2. Length Relationship:
The length of a simple pendulum affects its frequency. The formula for the frequency of a simple pendulum is:

f = 1/2π * √(g/L)

where g is the acceleration due to gravity and L is the length of the pendulum.

Since the lengths of the strings are LA and LB, we can write the equation as:

1/2π * √(g/LA) = 2 * (1/2π * √(g/LB))

Simplifying this equation, we get:

√(g/LA) = 2 * √(g/LB)

Squaring both sides of the equation, we have:

g/LA = 4 * (g/LB)

Simplifying further, we can cancel out g from both sides:

1/LA = 4 * (1/LB)

LA = LB/4

Conclusion:
From the analysis above, we can conclude that the correct answer is option 'C':

LA = LB/4, regardless of the masses.

This means that the length of the string for mass A is four times smaller than the length of the string for mass B, irrespective of the masses of the objects.

The periodic time (tp) is given by
  • a)
    ω / 2 π
  • b)
    2 π / ω
  • c)
    2 π × ω
  • d)
    π/ω
Correct answer is option 'B'. Can you explain this answer?

Divyansh Saha answered
Periodic time is the time taken for one complete revolution of the particle.
∴ Periodic time, tp = 2 π/ω seconds.

Under forced oscillation, the phase of the harmonic motion of the particle and phase of driving force
  • a)
    Are same
  • b)
    Are different
  • c)
    Both are zero
  • d)
    Not present
Correct answer is option 'B'. Can you explain this answer?

Harmonic motion is the natural motion of a body(we consider no air friction) under no force where as damped oscillation are under force hence the iscilation are different

Two simple pendulums of length 1m and 25 m, respectively, are both given small displacements in the same direction at the same instant.If they are in phase after the shorter pendulum has completed n oscillation, n is equal to 
  • a)
    4/3
  • b)
    5/4
  • c)
    7/5
  • d)
    8/7
Correct answer is option 'B'. Can you explain this answer?

Arya Reddy answered
∴ T ∝ √L , as time period decreases when the length of pendulum decreases, the time period of shorter pendulum (Ts) is smaller than that of longer pendulum (Tl). That means shorter pendulum performs more oscillations in a given time.
  It is given that after n oscillations of shorter pendulum, both are again in phase. So, by this time longer pendulum must have made (n – 1) oscillations. 
So, the two pendulum shall be in the same phase for the first time when the shorter pendulum has 
completed 5/4  oscillation  

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