Oscillations & Simple Harmonic Motion

Phase 1 – Page 2 | Multi-Concept IIT/JEE Solved Problems

                                                   
Simple harmonic motion iit material


Problem 9: Velocity–Displacement Relation

A particle executes SHM with amplitude A and angular frequency ω. Find the ratio of velocities at displacements x = A/2 and x = A/√2.

Solution:

Velocity in SHM:

v = ω√(A² − x²)

At x = A/2:

v₁ = ω√(A² − A²/4) = ωA√(3/4)

At x = A/√2:

v₂ = ω√(A² − A²/2) = ωA√(1/2)

Ratio:

v₁ : v₂ = √3 : √2


Problem 10: Energy at Given Displacement

A particle executes SHM with total energy E. Find its kinetic energy when displacement is A/2.

Solution:

Total energy:

E = ½mω²A²

Potential energy at x = A/2:

PE = ½mω²(A²/4) = E/4

Kinetic energy:

KE = E − E/4 = 3E/4


Problem 11: Phase Difference

What is the phase difference between velocity and acceleration in SHM?

Solution:

  • Velocity leads displacement by π/2
  • Acceleration is opposite to displacement

Phase difference between velocity and acceleration = π/2


Problem 12: Change in Time Period (Pendulum)

Length of a simple pendulum is increased by 21%. Find percentage change in time period.

Solution:

T ∝ √L

New length = 1.21L

T' = √1.21 T = 1.1T

Percentage increase = 10%


Problem 13: Mean Position Crossing

How many times does a particle cross mean position in one complete SHM?

Solution:

In one oscillation, the particle crosses mean position twice.

Answer: 2 times


Problem 14: Graph-Based Concept

Which graph is a straight line in SHM?

  • A) x vs t
  • B) v vs t
  • C) a vs x
  • D) KE vs t

Answer: C

Because:

a = −ω²x


Problem 15: Identifying Correct SHM Equation

Which of the following represents SHM?

  • A) a = +5x
  • B) a = −5x
  • C) a = constant
  • D) a ∝ v

Answer: B

IIT Trap:
Negative sign is mandatory for restoring force.


Problem 16: Maximum Acceleration

Find the maximum acceleration of a particle executing SHM.

Solution:

Acceleration:

a = −ω²x

Maximum at x = A:

amax = ω²A


Problem 17: Energy Graph Interpretation

At what position are kinetic and potential energies equal?

Solution:

KE = PE ⇒ x = A/√2

Answer: x = A / √2


IIT Thinking Summary (Page 2)

  • Use proportionality instead of full formulas
  • Energy method saves time
  • Graph questions are concept-based
  • Negative sign decides SHM

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