1. what are longitudinal waves

• A high pitched sound wave
• A low pitched sound wave

1. 

Longitudinal waves: 

A wave in which the particles of the medium vibrate back and forth in the same direction in which the wave is moving is called longitudinal wave. Example: sound waves.

or

In a longitudinal wave the particle displacement is parallel to the direction of wave propagation. See the figure below for further explanation.

2. 

The pitch of a sound is directly proportional to its frequency. Sounds of low frequency are said to have low pitch whereas sounds of high frequency are said to have high pitch.