Question
In an oscillating spring mass system, a spring is connected to a box filled with sand. As the box oscillates, sand leaks slowly out of the box vertically so that the average frequency $\omega(t)$ and average amplitude $A(t)$ of the system change with time t. Which one of the following options schematically depicts these changes correctly?
Options
Solution
At any point of time, time period is given by
$$T = 2\pi\sqrt{\frac{m}{k}}$$
Here $m$ is decreasing, so time period $T$ will be decreasing
Since $\omega = \frac{2\pi}{T}$
Hence as mass leaks, $\omega$ will increase
Now, at any instant
$$mg = kx_{0}$$
So, equilibrium length $x_{0} = \frac{mg}{k}$, where $m$ is decreasing
So, equilibrium length will decrease.
So, amplitude also go on decreasing.
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