On a slinky,we can produce:

$A$ person fires a gun standing at a distance of $55 \, m$ from a wall. If the speed of sound is $330 \, m s^{-1}$,find the time taken for an echo to be heard. (in $s$)

$(a)$ Briefly mention three uses of ultrasound in the field of medicine.
$(b)$ $A$ ship which is stationary is at a distance of $2800 \ m$ from the sea-bed. The ship sends an ultrasound signal to the sea-bed and its echo is heard after $4 \ s$. Find the speed of sound in water.

If the frequency of a tuning fork is $400 \, Hz$ and the speed of sound in air is $340 \, m s^{-1}$,find how far sound travels when the tuning fork makes $16$ vibrations. (in $, m$)

Give two applications of ultrasound.

In the bell jar experiment,as air is removed from the jar,