Asimple pendulum can be used as an altimeter on a plane. how will the period of the pendulum vary as the plane rises from the ground to its final cruising altitude?

As the plane rises, the distance between the pendulum and the center of the Earth increases which means that the force of gravity is decreased. With that, the swinging of the pendulum will be less restricted. The answer would be, the period of the pendulum will be greater. 

The period will increase as the altitude increases.

loudness of a sound varies with area of a vibrating body.

Explanation:

when a tuning fork is pressed against a rubber pad a feeble sound is heard because of the smaller area of pad but when a vibrating tuning fork is placed vertically on the table the surface area increases and so the loudness of a sound increases.