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All questions of Undamped Simple Harmonic Motion for EmSAT Achieve Exam

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. 
 

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.

 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.

The motion of simple pendulum is said to be S.H.M when its angle θ¸ through which bob is displaced from its equilibrium position is
  • a)
    θ is very small
  • b)
    θ is zero
  • c)
    θ is very large
  • d)
    θ = cosθ
Correct answer is option 'A'. Can you explain this answer?

Priya Patel answered
Consider a simple pendulum having mass 'm', length L and displaced by a small angle Θ with the vertical. Thus, it oscillates about its mean position. In the displaced position, two forces are acting on the bob, Gravitational force, which is the weight of the bob – 'mg' acting in the downward direction.

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

 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 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.

The instantaneous displacement of a simple harmonic oscillator is given by y = A cos (ωt + n/4). Its speed will be maximum at the time:). Its speed will be maximum at the time:
  • a)
    n/4ω
  • b)
    ω/n
  • c)
    ω/2n
  • d)
    2n/ω
Correct answer is option 'A'. Can you explain this answer?

Nandini Iyer answered
The instantaneous displacement of a simple pendulum oscillator is given as y = acos(ωt + π/4)
 
differentiating with respect to time,
dy/dt = -ωasin(ωt + π/4)
here, dy/dt is the velocity of a particle executing SHM.
so, speed of particle = | dy/dt | = ωasin(ωt + π/4)
so, dy/dt will be maximum when sin(ωt + π/4) will be maximum i.e., 1
so, sin(ωt + π/4) = 1 = sin(π/2)
⇒ωt + π/4 = π/2
⇒ωt = π/4
⇒t = π/(4ω)
hence, at t = π/(4ω) , speed of the particle will be maximum.
 

A simple pendulum is arranged using a small metallic bob of mass ‘m’and a light rubber cord of length ‘L’ (on suspending the bob), area of cross section ‘A’ and Young’s modulus ‘Y’. [One should use inextensible cord only for simple pendulum!]. When this unconventional pendulum is at rest in its mean position, the bob is pulled slightly down and is released. Then, the period of the vertical oscillation of the bob is (assuming that the size of the bob is negligible compared to the length of the cord):
  • a)
  • b)
  • c)
  • d)
Correct answer is option 'C'. Can you explain this answer?

Ciel Knowledge answered
The period as usual is given by T = 2n√(m/k). Here `m' is the same as the mass of the bob. The force constant can be found by writing the expression for Young's modulus (since it arises from the elastic force in the cord): V = FL/A(δL) where 6L is the increase in the length of the cord on pulling the bob down with a force F. Therefore, the force constant, F/(δL) = YA/L. On substituting this value, the period is 2m✓(mL/YA). 

Due to what force a simple pendulum remains in simple harmonic motion?
  • a)
    y, displacement
  • b)
    mg sinθ, component of weight due to gravitational force
  • c)
    a, acceleration
  • d)
    mg , weight
Correct answer is option 'B'. Can you explain this answer?

Preeti Iyer answered
For the pendulum, we can use Newton's second law to write an equation for the forces on the pendulum. The only force responsible for the oscillating motion of the pendulum is the x-component of the weight, so the restoring force on a pendulum is:
F=−mg sinθ
For angles under about 15°, we can approximate sinθ as θ and the restoring force simplifies to:
F ≈ −mgθ
Thus, simple pendulums are simple harmonic oscillators for small displacement angles.

The velocity and acceleration amplitudes of body executing simple harmonic motion is
  • a)
    ω2A , ωA
  • b)
    A , A
  • c)
    ω2/A , ω/A
  • d)
     ωA , ω2
Correct answer is option 'D'. Can you explain this answer?

Jayant Mishra answered
Maximum velocity :-
V = ωa   ,where ω is uniform angular velocity and a is the radius of the circle in which a reference particle executing S.H.M.
Velocity is maximum at mean positions. The maximum value of velocity is called velocity amplitude in SHM.
Acceleration is maximum at extreme position given by A = - ω 2a. The maximum value of acceleration is called acceleration amplitude in SHM.

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  

A uniform disc of mass m and radius R is pivoted smoothly at P,.If a uniform thin ring of mass m and radius R is welded at the lower point of the disc, find the period of SHM of the system (disc + ring).
  • a)
  • b)
  • c)
  • d)
Correct answer is option 'A'. Can you explain this answer?

Ishani Mehta answered
The time period of a physical pendulum is 
where, I = MI of the system about point of sduspension 
M = mass of the system and
l = distance between COM of the system and point suspension
 Now, M = m + m = 2m

A particle of mass m is allowed to oscillate on a smooth parabola x2 = 4ay, a > 0, about the origin O (see figure). For small oscillations, find the angular frequency ( ω )
  • a)
  • b)
  • c)
  • d)
Correct answer is option 'A'. Can you explain this answer?

Anushka Desai answered
During its oscillations, at a particular instant let the coordinates of the particle are (x, y)  The total energy of the particle is 
As oscillations are very small, we can ignore the middle term. 

A solid uniform cylinder of mass m performs small oscillations in horizontal plane if slightly displaced from its mean position shown in the figure. Initially springs are in naturals and cylinder does not slip on ground during oscillations due to friction between ground and cylinder. Force constant of each spring is k. The time period of oscillation is
  • a)
  • b)
  • c)
  • d)
Correct answer is option 'C'. Can you explain this answer?

Sai Mishra answered
A snapshot during oscillations of the cylinder is shown in the figure. Its displacement is x and velocity v. 
Its angular velocity is  ω = V/R(Due to pure rolling)
As the centre of the cylinder is at a distance x from the initial position, the spring which are connected at a
point on its rim must be compressed and stretched by a distance 2x. Thus, at this intermediate position total
energy of the oscillation system can be given as
 

In the figure is shown a small block B of mass m resting on a smooth horizontal floor and the block is attached to an ideal spring (of force constant k). The spring is attached to vertical wall W1. At a distance d from the block, right side of it, is present the vertical wall W2. Now, the block is compressed by a distance 5d/3 and released. It starts oscillating. If the  collision of the block with W2 are perfectly elastic, the time period of oscillation of the  block is
 
 
  • a)
  • b)
  • c)
  • d)
Correct answer is option 'A'. Can you explain this answer?

Gargi Sharma answered
 absence of wall W2, the time period of block would have been  But due to the presence of W2, it alters. But for the left part of oscillation (from the mean position shown), the period will be 
For the right side part, d = A sinω t [from x = A sinω t ] 
This is the time taken by the block to reach W2 from mean position. Collision with W2 is perfectly elastic (given). 
Time taken for right side part of oscillation will be 
∴ Total time period is 
 

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