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NEET PHYSICSOscillationsMedium

Question

A mass of 2.0 kg2.0\text{ kg} is put on a flat pan attached to a vertical spring fixed on the ground as shown in the figure. The mass of the spring and the pan is negligible. When pressed slightly and released, the mass executes a simple harmonic motion. The spring constant is 200 N/m200\text{ N/m}. What should be the minimum amplitude of the motion, so that the mass gets detached from the pan? (Take g=10 m/s2g=10\text{ m/s}^2)

A

8.0 cm

B

10.0 cm

C

any value less than 12.0 cm

D

4.0 cm

Step-by-Step Solution

  1. Identify Condition for Detachment: The mass will detach from the pan when the contact force (Normal Reaction, NN) between the mass and the pan becomes zero. This happens when the downward acceleration of the pan equals the acceleration due to gravity (gg). If the pan accelerates downwards faster than gg, the mass (which falls at gg under gravity alone) will lose contact.
  2. Analyze Motion: In a vertical spring-mass system, the maximum downward acceleration occurs at the highest point of the oscillation (extreme position). The magnitude of maximum acceleration in SHM is given by amax=ω2Aa_{max} = \omega^2 A .
  3. Set Condition: For detachment, amaxga_{max} \ge g. The minimum amplitude occurs when amax=ga_{max} = g. ω2A=g\omega^2 A = g
  4. Substitute ω\omega: We know ω2=km\omega^2 = \frac{k}{m} . Therefore: kmA=g\frac{k}{m} A = g A=mgkA = \frac{mg}{k}
  5. Calculate Value: Given m=2.0 kgm = 2.0\text{ kg}, g=10 m/s2g = 10\text{ m/s}^2, and k=200 N/mk = 200\text{ N/m}. A=2.0×10200=20200=0.1 mA = \frac{2.0 \times 10}{200} = \frac{20}{200} = 0.1\text{ m} A=10.0 cmA = 10.0\text{ cm}

Exam Context & Concepts Covered

This question aligns with the NEET PHYSICS syllabus, specifically targeting concepts from Oscillations. Mastering this topic is crucial for scoring well in the upcoming medical entrance examinations. Solving conceptually related problems will help you understand the nuances of these concepts and improve your problem-solving speed.

PHYSICSOscillationsattachedverticalspringgroundfigure

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