Class 11 Physics Chapter 13: Oscillations MCQs with answers

Answer: (c) periodic but not oscillatory

The tip goes round a circle and returns to the same point after every revolution, so the motion is periodic. It does not move to and fro about a mean position, so it is not oscillatory; circular motion is the standard example of a periodic motion that is not oscillatory.

Answer: (a) 60

A frequency of 0.5 Hz is 0.5 oscillation per second. In 2 min = 120 s it makes 0.5 × 120 = 60 oscillations. 240 divides 120 s by 0.5; 120 counts seconds, not oscillations.

Answer: (d) 31.4 rad s⁻¹

ω = 2π/T = 2π/0.2 = 10π ≈ 31.4 rad s⁻¹. 5 rad s⁻¹ is the frequency 1/T, not ω; 15.7 rad s⁻¹ uses π/T; 1.26 rad s⁻¹ multiplies 2π by T.

Answer: (b) 4 cm

In one complete oscillation the particle goes from A to −A and back, a path of 4A. So 3 × 4A = 48 cm and A = 4 cm. 16 cm is the path per oscillation; 8 cm takes the path per oscillation as 2A.

Answer: (d) decrease and increase

The speed is greatest at x = 0 and zero at the extremes, so it decreases. The acceleration is −ω²x, whose magnitude grows with the distance from the mean position, so it increases.

Answer: (a) π

With x = A cos ωt, a = −ω²A cos ωt = ω²A cos(ωt + π); the acceleration plot differs in phase from the displacement plot by π. π/2 is the phase difference between displacement and velocity.

Answer: (c) 1 s

K = ½kA² sin²(ωt + φ). Since the sign of v does not matter in K, K repeats twice in each oscillation, so its period is T/2 = 1 s. 2 s confuses the period of K with that of x.

Answer: (b) becomes four times

E = ½kA². With k unchanged, doubling A multiplies E by 2² = 4.

Answer: (d) stays the same

T = 2π√(m/k) contains neither the amplitude nor the energy; the period of SHM does not depend on the amplitude.

Answer: (a) 10%

T ∝ √L, so T′/T = √1.21 = 1.1: an increase of 10%. 21% treats T as proportional to L; 42% doubles the change instead of halving it.