All questions of Simple Harmonic Motion (Oscillations) for JEE Exam

A particle executes simple harmonic motion between x = -A and x = +A. The time taken for it to go from 0 to A/2 is T1 and to go from A/2 to A is T2. Then
  • a)
    T1 < T2
  • b)
    T1 > T2
  • c)
    T1 = T2
  • d)
    T1 = 2T2
Correct answer is option 'A'. Can you explain this answer?

Diya Iyer answered
= T2

This statement is not necessarily true. The time taken for the particle to go from 0 to A/2 and from A/2 to A may not be equal in general.

However, if the motion is symmetric about x=0 (i.e., the particle takes the same amount of time to go from 0 to A/2 as it does from 0 to -A/2), then T1 = T2. This is because the total time period of the motion is T = 2T1 = 2T2, and the particle spends half of this time period in each half of the motion, so T1 = T2 = T/2.

A particle moves with simple harmonic motion in a straight line. In first τ s, after starting from rest it travels a distance a, and in next τ s it travels 2a, in same direction, then:
  • a)
    amplitude of motion is 3a
  • b)
    time period of oscillations is 8τ
  • c)
    amplitude of motion is 4a
  • d)
    time period of oscillations is 6τ
Correct answer is option 'D'. Can you explain this answer?

Disha Mishra answered
In simple harmonic motion, starting from rest,
At t = 0 , x = A
x = Acosωt ..... (i)
When t = τ , x = A – a
When t = 2 τ , x = A –3a
From equation (i)
A – a = Acosω τ ......(ii)
A – 3a = A cos2ω τ ......(iii)
As cos2ωτ = 2 cos2 ωτ – 1 …(iv)
From equation (ii), (iii)  and (iv)
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A highly rigid cubical block A of small mass M and side L is fixed rigidly on to another cubical block B of the same dimensions and of low modulus of rigidity η such that the lower face of A completely covers the upper face of B. The lower face of B is rigidly held on a horizontal surface. A small force F is applied perpendicular to one of the sides faces of A. After the force is withdrawn, block A executes small oscillations the time period of which is given by
  • a)
  • b)
  • c)
  • d)
Correct answer is option 'D'. Can you explain this answer?

Mira Roy answered
NOTE : When a force is applied on cubical block A in the horizontal direction then the lower block B will get distorted as shown by dotted lines and A will attain a new position (without distortion as A is a rigid body) as shown by dotted lines.
For cubical block B
⇒ F = ηLΔL
ηL is a constant
⇒ Force F ∝ ΔL and directed towards the mean position, oscillation will be simple harmonic in nature.
Here, Mω2 = ηL

A child swinging on a swing in sitting position, stands up, then the time period of the swing will
  • a)
    increase
  • b)
    decrease
  • c)
    remains same
  • d)
    increases of the child is long and decreases if the child is short
Correct answer is option 'B'. Can you explain this answer?

Rithika Mishra answered
Let the spring constant of the original spring be k. Then its time period   where m is the mass of
oscillating body.
When the spring is cut into n equal parts, the spring constant of one part becomes nk. Therefore the new time period,

A point mass is subjected to two simultaneous sinusoidal displacements in x-direction, x1(t) = A sin wt and x2(t) =  Adding a third sinusoidal displacement x3(t) = B sin (ωt + φ) brings the mass to a complete rest. The values of B and φ are
  • a)
  • b)
  • c)
  • d)
Correct answer is option 'B'. Can you explain this answer?

Bhavya Joshi answered
Two sinusoidal displacements have amplitude A each, with a phase difference of   It is given that sinusoidal displacement x3(t) brings the mass to a complete rest. This is possible when the amplitude of third is A and is having a phase difference of  with
respect to x1 (t) as shown in the figure.

A particle executes simple harmonic motion with a frequency. f. The frequency with which its kinetic energy oscillates is
  • a)
    f/2
  • b)
    f
  • c)
    2f
  • d)
    4f
Correct answer is option 'C'. Can you explain this answer?

Devansh Joshi answered
NOTE : During one complete oscillation, the kinetic energy will become maximum twice.
Therefore the frequency of kinetic energy will be 2f.

The x-t graph of a particle undergoing simple harmonic motion is shown below. The acceleration of the particle at t = 4 / 3 s is
  • a)
  • b)
  • c)
  • d)
Correct answer is option 'D'. Can you explain this answer?

Nandini Nair answered
From the graph it is clear that the amplitude is 1 cm and the time period is 8 second. Therefore the equation for the S.H.M. is
The velocity (v) of the particle at any instant of time ‘t’ is
The acceleration of the particle is

The mass M shown in the figure oscillates in simple harmonic motion with amplitude A. The amplitude of the point P is
  • a)
  • b)
  • c)
  • d)
Correct answer is option 'D'. Can you explain this answer?

Rounak Desai answered
In case (ii), the springs are shown in the maximum compressed position. If the spring of spring constant k1 is compressed by x1 and that of spring constant k2 is compressed by x2 then
x1 + x= A … (i)

The function x = A sin2 ωt + B cos2 ωt + C sin ωt cosωt represent SHM for which of the option(s)
  • a)
    for all value of A, B and C (C ≠ 0)
  • b)
    A = B, C = 2B
  • c)
    A = -B, C = 2B
  • d)
    A = B, C = 0
Correct answer is option 'A,B,C'. Can you explain this answer?

The  given equation is
x = A sin2 ωt + B cos2 ωt + C sin ωt cos ωt
NOTE THIS STEP
Rearranging the equation in a meaningful form (for interpretation of SHM)

The above equation is that of SHM with amplitude C/2 and angular frequency 2ω. Thus option (a) is correct.
(b) If A = B and C = 2B then x = B + B sin 2ωt
This is equation of SHM. The mean position of the particle executing SHM is not at the origin.
Option (b) is correct.
(c) A = – B, C = 2B; Therefore
x = B cos 2ωt + B sin 2ωt
Let B = X cos φ = X sin φ then
x = X sin 2ωt cos φ + X cos 2ωt sin φ This represents equation of SHM.
(d) A = B, C = 0 and x = A.
This equation does not represents SHM.

A uniform rod of length L  and mass M is pivoted at the centre. Its two ends are attached to two springs of equal spring constants k. The springs are fixed to rigid supports as shown in the figure, and the rod is free to oscillate in the horizontal plane.
The rod is gently pushed through a small angle θ in one direction and released. The frequency of oscillation is
  • a)
  • b)
  • c)
  • d)
Correct answer is option 'C'. Can you explain this answer?

Jatin Dasgupta answered
Figure shows the rod at an angle θ with respect to its equilibrium position. Both the springs are stretched by length
The restoring torque due to the springs τ = – 2 (Restoring force) × perpendicular distance
    ... (i)
If I is the moment of inertia of the rod about M then
    … (ii)
From (i) & (ii) we get
Comparing it with the standard equation of rotational SHM we get

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