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 (t) and average amplitude A(t) of the system change with time t. Which one of the following options schematically depicts these changes correctly?
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Answer
(4) [figure]
Solution
Angular frequency of the spring–mass system: = km
As sand leaks out, m decreases ⇒ (t) increases gradually from its initial (non-zero) value.
The leaking sand carries away its kinetic energy, so the energy of the oscillator E = 12kA2 decreases.
∵ k is constant ⇒ the amplitude A(t) decreases gradually.
∴ (t) rises and A(t) falls with time, as shown in option (4).
Answer: (4)