A point `A` oscillates according to a certain harmonic law in the reference frame `K^(')` which in its turn performs harmonic oscillations relative to the reference frome` K`. Both oscillations occur along the same direction. When the `K^(')` frame oscillates at the frequency 20 or `24 Hz`, the beat frequency of the point `A` in the `K` frame turns out to be equal to `v`. At what frequency of oscillation of the frame `K^(')` will the beat frequency of the point `A` become equal to `2v`?

Explanation

If the frequency of `A` with respect to `K^(')` is `v_(0)` and `K^(')` oscillates with frequency `bar v` with respect to `K`, the beat frequency of the point `A` in the `K-` framce will be `v` when
`bar(v)=v_(0)+-v`
In the present case `bar(v)=20` and 24. This means
`v_(0)=22. & v=2` ,brgt Thus beats of `2 v=4` will be heard when `bar(v)=26 ` or 18.