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All questions of Simple Harmonic Motion (SHM) and Oscillations for JEE 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.

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.

The dimensions and unit of phase constant Φ is
  • a)
    dinensionless,rad
  • b)
    [T]-1 ,s-1
  • c)
    dinensionless, no units
  • d)
    [T] , s
Correct answer is option 'A'. Can you explain this answer?

Suresh Reddy answered
Mathematical constants don't have any dimensions hence, it is dimensionless and phase constant is in angle therefore, the unit is radian.

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 .

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.

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 sign in equation F = -kx is changed what would happen to the motion of the oscillating body?
  • a)
    Motion would be linearly accelerated motion
  • b)
    Body would come at rest
  • c)
    Body would slow down
  • d)
    Motion would be oscillating accelerated
Correct answer is option 'A'. Can you explain this answer?

Imk Pathsala answered
If the sign is changed in F=-kx then the force and hence acceleration will not be opposite to the displacement. Due to this the particle will not oscillate and would accelerate in the direction of displacement. Hence the motion of the body will become linearly accelerated motion.

A rubber ball with water, having a small hole in its bottom is used as the bob of a simple pendulum. The time-period of such a pendulum:
  • a)
    Increases with time
  • b)
    First increases and then decreases finally having same value as at the beginning
  • c)
    Decreases with time
  • d)
    Is a constant
Correct answer is option 'B'. Can you explain this answer?

Rajesh Gupta answered
When rubber ball completely filled with water its centre of gravity will be at its centre, as water will fall through hole its COG will shift towards lower side leading to increase in length of pendulum and thus T, when very small amount of water will be left in rubber ball its COG will again shifts upward causing decrease in length and thus T, and finally when rubber ball becomes empty its COG will be at its centre and T will remains same as earlier.

A particle starts S.H.M. from the mean position. Its amplitude is A and time period is T. At the time when its speed is half of the maximum speed, its displacement y is
  • a)
    A√3/2
  • b)
    2A/√3
  • c)
    A/2
  • d)
    A/√2
Correct answer is option 'A'. Can you explain this answer?

Rajesh Gupta answered
The relation between angular frequency and displacement is given as
v=ω√A2−x2
Suppose
x=A sinω t
On differentiating the above equation w.r.t. time we get
dx/dt​=Aωcosωt
The maximum value of velocity will be [{v{\max }} = A\omega \]
The displacement for the time when speed is half the maximum is given as
v=Aω/2
A2ω2=4ω(A2−x2)
By substituting the value in (1) we get the displacement as
x=A√3/2

Damped natural frequency is
  • a)
    same as natural frequency
  • b)
    lower than natural frequency
  • c)
    higher than natural frequency
  • d)
    none of the above
Correct answer is option 'B'. Can you explain this answer?

Geetika Shah answered
If a resonant mechanical structure is set in motion and left to its own devices, it will continue to oscillate at a particular frequency known as its natural frequency, or "damped natural frequency". This will be a little lower in frequency than the resonant frequency, which is the frequency it would assume if there were no damping. The resonant frequency is also called the "undamped natural frequency”

In a simple pendulum the restoring force is due to
  • a)
     The tangential component of the gravitational force
  • b)
    The radial component of the gravitational force
  • c)
    The tangential component of the tension in string
  • d)
    The radial component of the tension in string
Correct answer is option 'A'. Can you explain this answer?

Pooja Shah answered
In a simple pendulum the restoring force is due to the tangential component of the gravitational force because on applying torque equation on the radial forces the effect is nullified due to it passing from centre & only tangential component remains.

The equation of motion of a particle is x= 3cos(0.45t+π/4)m. Its maximum acceleration is
  • a)
    0.60 ms-2
  • b)
    0.50 ms-2
  • c)
    0.55 ms-2
  • d)
    0.45 ms-2
Correct answer is option 'A'. Can you explain this answer?

Nilotpal Singh answered
+ 2) meters.

We can find the velocity and acceleration functions by taking the first and second derivatives of x with respect to time:

velocity v(t) = dx/dt = -3(0.45)sin(0.45t + 2)

acceleration a(t) = d^2x/dt^2 = -3(0.45)^2cos(0.45t + 2)

To find the maximum velocity, we set v(t) equal to zero and solve for t:

0 = -3(0.45)sin(0.45t + 2)

sin(0.45t + 2) = 0

0.45t + 2 = nπ, where n is an integer

t = (nπ - 2)/0.45

To find the maximum acceleration, we set a(t) equal to zero and solve for t:

0 = -3(0.45)^2cos(0.45t + 2)

cos(0.45t + 2) = 0

0.45t + 2 = (n + 0.5)π, where n is an integer

t = [(n + 0.5)π - 2]/0.45

Note that there are infinitely many solutions for both t_max_v and t_max_a, as there are infinitely many values of n.

To find the values of maximum velocity and maximum acceleration, we can substitute the values of t_max_v and t_max_a into the corresponding velocity and acceleration functions:

v_max = -3(0.45)sin(0.45t_max_v + 2)

a_max = -3(0.45)^2cos(0.45t_max_a + 2)

However, since there are infinitely many solutions for t_max_v and t_max_a, we cannot find a unique value for v_max and a_max without additional information.

 At what distance from the mean position would the K.E of a particle in simple harmonic motion be equal to its potential energy?
  • a)
    a/√2
  • b)
    a/2
  • c)
    2√a
  • d)
    a
Correct answer is option 'A'. Can you explain this answer?

Raghav Bansal answered
Let say from some distance x, the KE = PE and as total energy must be conserved and TE = -½ kA2
Thus we get 2PE = ½ kA2
Thus we get 2kx2 = kA2
We get x = A / √2

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.

The kinetic energy of a body executing S.H.M. is 1/3 of the potential energy. Then, the displacement of the body is x percent of the amplitude, where x is
  • a)
    33
  • b)
    50
  • c)
    67
  • d)
    87
Correct answer is option 'A'. Can you explain this answer?

Pooja Shah answered
We know that PE + KE = TE = constant
Hence at the extremis TE = PE = ½ kz2  
Where z is amplitude and k is shm constant.
Thus when KE = ⅓ PE
We get PE = ¾ TE =  ½ kz2
Hence we get  ½ kx2 = ¾  ½ kz2
We get x/z = √3/4 
= 1.73 / 2
= .87
Thus we get x is 87 percent of the amplitude.

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 particle of mass 10 gm lies in a potential field v = (50x2+100) J/kg. The value of frequency of oscillations in cycle/sec is
  • a)
    5/π
  • b)
    50/π
  • c)
    10/π
  • d)
    100/π
Correct answer is option 'A'. Can you explain this answer?

Correct option: A
Mass is m = 10 g = 0.01 kg.
The actual potential energy is U = m × (potential per unit mass); the quadratic contribution is Uq = 50 m x2.
Compare with U = (1/2) k x2. Thus (1/2) k = 50 m, so k = 100 m.
Angular frequency satisfies ω² = k/m. Substituting gives ω² = 100, hence ω = 10 rad s-1.
Frequency is f = ω / (2π) = 10 / (2π) = 5/π Hz. Therefore option A is correct.

The pendulum of a wall clock executes
  • a)
    a translatory motion
  • b)
    a rotary motion
  • c)
    a random motion
  • d)
    an oscillatory motion
Correct answer is option 'D'. Can you explain this answer?

Chirag Mehta answered
The bob of a pendulum moves in such a way that it repeats its positions several time but alternately the time gap between these positions is always equal which proves that the motion of a pendulum is oscillatory.

Choose the correct time period of the function sin ωt + cos ωt
  • a)
    π/8ω
  • b)
    2π/ω
  • c)
    π/4ω
  • d)
    π/2ω
Correct answer is option 'B'. Can you explain this answer?

Understanding the Function
The function given is sin(ωt) + cos(ωt). To determine the period of this function, we need to analyze its components.
Components of the Function
- The sine function, sin(ωt), has a standard period of 2π.
- The cosine function, cos(ωt), also has a period of 2π.
Since both functions share the same frequency, the overall period of their sum will also be 2π.
Calculating the Period
1. Period of Sine Function:
- The period is given by T = 2π/ω.
2. Period of Cosine Function:
- Similarly, the period is also T = 2π/ω.
Since both functions oscillate with the same frequency, the resultant function sin(ωt) + cos(ωt) will also have a period of 2π/ω.
Correct Option
Thus, the correct answer for the time period of the function sin(ωt) + cos(ωt) is:
- Option B: 2π/ω
This means that every 2π/ω seconds, the function will complete one full cycle.
Conclusion
In summary, the periodic behavior of both sine and cosine functions, when combined, maintains the same period of 2π/ω. Therefore, recognizing these fundamental properties allows us to confidently determine the period of the combined function.

If the maximum velocity and acceleration of a particle executing S.H.M are equal in magnitude, the time period will be
  • a)
    6.28 s
  • b)
    1.57 s
  • c)
    3.14 s
  • d)
    12.56 s
Correct answer is option 'A'. Can you explain this answer?

Jyoti Dey answered
**Explanation:**

When a particle is executing Simple Harmonic Motion (SHM), its displacement from the mean position follows a sinusoidal function. The maximum displacement of the particle is called the amplitude (A) of the motion. The particle oscillates back and forth between two extreme positions, which are equal in magnitude but opposite in direction.

The time taken for one complete oscillation of the particle is called the time period (T) of the motion. It is the time taken for the particle to go from one extreme position to the other and back again.

The maximum velocity (vmax) of the particle occurs when the particle passes through the mean position (equilibrium position). At this point, the velocity is at a maximum and is in the same direction as the acceleration. The maximum acceleration (amax) of the particle occurs when the particle is at its extreme positions. At these points, the acceleration is at a maximum and is in the opposite direction to the displacement.

If the maximum velocity and acceleration of the particle are equal in magnitude, it means that the amplitude of the motion is equal to the acceleration. Mathematically, this can be represented as:

amax = vmax

Using the equations of SHM, we can relate the amplitude, time period, maximum velocity, and maximum acceleration as follows:

amax = ω^2 A

vmax = ω A

where ω is the angular frequency of the motion.

Since amax = vmax, we can equate the above two equations:

ω^2 A = ω A

Simplifying the equation:

ω^2 = ω

ω = 1

The angular frequency ω is related to the time period T by ω = 2π/T. Substituting this value into the equation:

(2π/T)^2 = 2π/T

Simplifying the equation:

4π^2/T^2 = 2π/T

2π/T = 4π^2/T^2

T = 2

Therefore, the time period of the motion is T = 2 seconds, which is equivalent to 6.28 seconds (approximately). Hence, the correct answer is option A: 6.28 s.

A particle executes SHM of time period T, the time period with which the total energy changes is
  • a)
    2T
  • b)
    T
  • c)
    T/2
  • d)
    Infinite
Correct answer is option 'D'. Can you explain this answer?

Kavita Joshi answered
Potential energy is a function of height. Now the motion of a simple pendulum can be expressed in terms of the angle at which the string makes with the normal (the angle it would hang at if it didn't swing.)Now Because the bob of the pendulum is always in motion except at the two turning points where the angle is at a maximum (and even at these points the bob is only motionless at one instant in time but for no inteval) the hight is always changing for every inteval of time and thus the potential energy is always changing.Also the potential energy is the same for all values of the angle that have the same magnatude (independent of the sign.)

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?

Lavanya Menon answered
The phenomenon of increase in amplitude when the driving force is close to the natural frequency of the oscillator is known as resonance. By the definition of resonance.

For all practical purposes, the motion of a simple pendulum is SHM,
  • a)
    None of these
  • b)
    Only if the length of its string is at least one meter
  • c)
    Only if the maximum angle which its string makes with the vertical is less than 342.
  • d)
    Only if the maximum angle which the string makes with the vertical is less than I
Correct answer is option 'A'. Can you explain this answer?

Nitin Nair answered
The motion of Simple Pendulum as Simple Harmonic Motion. When we pull a simple pendulum from its equilibrium position and then release it, it swings in a vertical plane under the influence of gravity. It begins to oscillate about its mean position. Therefore, the motion is periodic and oscillatory.
SO OPTION A IS CORRECT.

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

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.

Energy is supplied to the damped oscillatory system at the same rate at which it is dissipating energy, then the amplitude of such oscillations would become constant. Such oscillations are called
  • a)
    Damped oscillations
  • b)
    Undamped oscillations
  • c)
    Coupled oscillations
  • d)
    Maintained oscillations
Correct answer is option 'D'. Can you explain this answer?

Anoushka Basu answered
Energy is supplied to the damped oscillatory system at the same rate at which it is dissipating energy, and then the amplitude of such oscillations would become constant. Such oscillations are called maintained oscillations. By the definition of maintained oscillations.

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