A mass of $2.0 \mathrm{~kg}$ is put on a flat pan attached to a vertical spring fixed on the ground as shown…

A mass of $2.0 \mathrm{~kg}$ 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 $200 \mathrm{~N} / \mathrm{m}$. What should be the minimum amplitude of the motion so that the mass gets detached from the pan (take $g=10 \mathrm{~m} / \mathrm{s}^2$ ).
  1. $10.0 \mathrm{~cm}$
  2. any value less than $12.0 \mathrm{~cm}$
  3. $4.0 \mathrm{~cm}$
  4. $8.0 \mathrm{~cm}$

Solution

For given condition $\begin{aligned} m g & =m \omega^2 a=K a \\ \Rightarrow \quad a & =\frac{m g}{k}=\frac{2 \times 10}{200} \\ & =0.1 \mathrm{~m}=10 \mathrm{~cm} \end{aligned}$ *

Asked in: NEET 2007

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