A marble is allowed to roll down an inclined plane from a fixed height. At the foot of inclined plane, it moves on horizontal surface. a) Covered with silk b) Covered with a layer of sand c ) Covered with glass sheet . On which surface marbles move the shortest distance. Give reason for your answer.

The frequency of a tuning fork can be found by the method shown. a long tube open at both ends is submerged in a beaker of water, and the vibrating tuning fork is placed near the top of the tube. the length l of the air column is adjusted by moving the tube vertically. the sound waves generated by the fork are reinforced when the length of the air column corresponds to one of the resonant frequencies of the tube. the smallest value for l for which a peak occurs in sound intensity is 7 cm. l what is the frequency of the tuning fork? the speed of sound in air is 345 m/s. answer in units of hz