a light pointer fixed to one prong of a tuning fork touches a vertical plate .The fork is set vibrating and the plate is allowed to fall freely.eight complete oscillations are counted when the plate falls through 10cm , then the frequency of fork is

Here we see that plate falls by a distance of 0.1m first we find in what time did plate take to fall 10cm . Same amount of time the fork would have taken to complete oscilattion .Required time is √2h/g. solving √0.02 s .Fork takes this time for 8 oscillation so then we know the time which it taje to complete on oscillation that is time period invese the value we will find frequency I.e. 40√2