Oscillations & Simple Harmonic Motion

IIT / JEE Tough Objective Paper – 3


Q1. SHM with Energy Constraint

A particle executes SHM. At what displacement is the ratio of kinetic energy to potential energy equal to 1 : 3 ?

Solution:

KE : PE = 1 : 3 ⇒ KE = (1/4)E, PE = (3/4)E

PE / E = x² / A² ⇒ x² / A² = 3/4 ⇒ x = (√3/2)A

Answer: x = (√3/2)A


Q2. Time Calculation Trap

Time taken by a particle to move from displacement A/2 to mean position is:

Answer: T/12

JEE Trick:
Use phase method, not equations.
x = A cosθ → A/2 ⇒ θ = π/3
Mean ⇒ θ = π/2
Δθ = π/6 ⇒ Δt = (T/2π)(π/6) = T/12


Q3. Non-SHM Identification

Which of the following motions is NOT SHM?

  • A) Small oscillations of pendulum
  • B) Block on spring
  • C) Circular motion projected on diameter
  • D) Large angle pendulum motion

Correct Answer: D

Reason: Restoring force not proportional to displacement at large angles.


Q4. Acceleration Direction Trap

At a point between mean and extreme position, acceleration is:

  • A) Zero
  • B) Towards mean
  • C) Away from mean
  • D) Random

Correct Answer: B

IIT Rule: Acceleration always points toward mean position.


Q5. Combined Motion

A particle performs SHM along x-axis and uniform motion along y-axis. The resultant path is:

  • A) Circle
  • B) Ellipse
  • C) Straight line
  • D) Cycloid

Correct Answer: B


Q6. Maximum Velocity Location

Velocity is maximum when:

  • A) x = A
  • B) x = A/2
  • C) x = 0
  • D) x = −A

Correct Answer: C


Q7. Dimensional Analysis (Advanced)

Which expression gives time period dimensionally?

  • A) √(k/m)
  • B) √(m/k)
  • C) m/k
  • D) k/m

Correct Answer: B


Q8. Energy Graph Concept

Which graph is linear?

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

Correct Answer: C

Because a = −ω²x


Q9. Frequency Change

If spring constant becomes 4k, frequency becomes:

Answer: 2 times

Since f ∝ √k


Q10. Ultimate IIT Trap

A particle passes through mean position with speed v. What is speed at displacement A/2?

Solution:

v_max = ωA v = ω√(A² − (A/2)²) = ωA√(3/4) = (√3/2)v_max

Answer: (√3/2)v


IIT LEVEL TAKEAWAY:
• Phase method saves time
• Energy ratio → square relation
• Acceleration always toward mean
• Large angles break SHM


IIT Tough Objective Paper – 3 Completed ✅

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