Answer:
Explanation:
Provided:
The trolley, with mass M, is allowed to roll freely without friction.
The coefficient of friction between the trolley and mass m is
.
A force F is applied to mass m.
The acceleration of the system is

The frictional force will counterbalance the weight of the block.
The frictional force is 





The intensity of the sound increases because sound waves are mechanical waves, meaning they cannot move through a vacuum and require a medium to propagate.