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PhysicsMediumClass 11

Equation of SHM — x = A sin(ωt+φ)

SHM

8

JEE Qs

8%

Hard

60

min

Master the determination of the initial phase constant (φ) from given initial conditions (position and velocity at t=0) as it is fundamental to solving SHM problems.

🧮 Key Formulas

x = A sin(ωt + φ)
v = dx/dt = Aω cos(ωt + φ)
a = dv/dt = -Aω^2 sin(ωt + φ)
a = -ω^2 x
v = ±ω sqrt(A^2 - x^2)
ω = 2π/T = 2πf

✅ Key Points for JEE

  • 1The equation x = A sin(ωt + φ) describes the position of a particle executing SHM, where A is amplitude, ω is angular frequency, and φ is the initial phase constant.
  • 2The phase constant (φ) is crucial for determining the initial state of the oscillator (position and velocity at t=0) and must be carefully calculated using both initial position and initial velocity.
  • 3Velocity (v) leads position (x) by π/2, and acceleration (a) leads velocity (v) by π/2 (or position by π) in SHM; understanding these phase relationships is vital for problem-solving.
  • 4The defining characteristic of SHM is the linear restoring force or acceleration proportional to displacement and directed towards the equilibrium position: a = -ω^2 x.
  • 5The choice between a sine or cosine function for displacement is arbitrary; the phase constant φ will adjust accordingly to represent the same physical motion.

⚠️ Common Mistakes

  • Incorrectly determining the initial phase constant (φ), especially failing to consider the sign of initial velocity or choosing the wrong quadrant for φ.
  • Confusing the total phase (ωt + φ) with the initial phase constant (φ) in problem interpretation.
  • Forgetting that all angles (phases) in trigonometric functions must be in radians for the equations to be consistent, particularly when ωt is calculated.
  • Incorrectly assuming that x = A at t=0 or v = 0 at t=0 unless specified, which is only true for specific initial phase constants.

📝 Practice Questions

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Q36.A particle oscillates along the x-axis according to the law, x(t) = x0 sin2 ( 2t ) where x0 = 1 m . The kinetic energy (K) of the particle as a function of x is correctly represented by the graph (1) (2) (3) (4)

2025·Graph basedMedium

Q28.Two bodies A and B of equal mass are suspended from two massless springs of spring constant k1 and k2 , respectively. If the bodies oscillate vertically such that their amplitudes are equal, the ratio of the maximum velocity of A to the maximum velocity of B is (1) k1 (2) k2 √k1k2 (3) (4) k2 k1 √k2k1

2025·MCQEasy

Q41.A light hollow cube of side length 10 cm and mass 10 g , is floating in water. It is pushed down and released to execute simple harmonic oscillations. The time period of oscillations is yπ × 10−2 s, where the value of y is (Acceleration due to gravity, g = 10 m/s2 , density of water = 103 kg/m3 ) 2025 (23 Jan Shift 1) JEE Main Previous Year Paper (1) 6 (2) 2 (3) 4 (4) 1

2025·NumericalMedium

Q36.A particle is executing simple harmonic motion with time period 2 s and amplitude 1 cm . If D and d are the total distance and displacement covered by the particle in 12.5 s , then D is d (1) 16 (2) 10 5 (3) 15 (4) 25 4

2025·MCQMedium

Q35.Given below are two statements. One is labelled as Assertion (A) and the other is labelled as Reason (R). Assertion (A) : Knowing initial position x0 and initial momentum p0 is enough to determine the position and momentum at any time t for a simple harmonic motion with a given angular frequency ω. Reason (R): The amplitude and phase can be expressed in terms of x0 and p0 . In the light of the above statements, choose the correct answer from the options given below : (1) (A) is false but (R) is true (2) (A) is true but (R) is false (3) Both (A) and (R) are true but (R) is NOT the (4) Both (A) and (R) are true and (R) is the correct correct explanation of (A) explanation of (A)

2025·Assertion ReasoningMedium

Q24.The displacement of a particle executing SHM is given by x = 10 sin (wt + π3 )m. The time period of motion is 3.14 s. The velocity of the particle at t = 0 is ______ m/s.

2024·NumericalEasy

NCERT Chapters

  • Class 11 Physics Ch 14: Oscillations