Question

A short flute produces a higher pitch sound than a long pipe

Answer 1

Flute which is a tube which oscillates making longitudinal waves call sound.

Tubes which has a fundamental pitch linked to a wave vibrating over length.  

Whether sound is produced as transverse mouthpiece, reed or brass mouthpiece.  

It is confirmed by length of tube.

Simple tube will have single pitch illustrated in other answer with pan pipe.

Answer 2

When the length of a organ pipe is changed, it will vibrate with a different frequencies .

Shorter pipe have higher frequency and therefore higher pitch.

When a $\textbf{musician}$ presses their finger on a hole of pipe /flute , they shorten its length. The more fingers they add to the pipe , the shorter they make it, and the higher the pitch will be.

$\textbf{so, a short flute produces a higher }\\\textbf{ pitch sound than a long}\\\textbf{ flute /pipe.}$