Question

explain how pinna is a vestigial organ.

Answer 1

yes , pinna is the vestigal organ , it donot have any function , it only gives ear a shape , nothing else , sound will generate form a source and it will move in the auditary nreves , so, pinna donot have any work in the mechanism of hearing . 

so, due to that its considered as a vestigal organ . 
HOPE IT CLEARS NOW

Answer 2

Pinna is called as external ear,It is vestigeal organ. But exactly speaking muscles of pinna are vestigial, so we can not move the external ear pinna. ... Coming to the point, the function of pinna is to collect sound waves and pass it to the auditory canal of the ear and then to the ear drum.