Question

an object can have zero average velocity but cannot have zero average speed justify

Answer 1

velocity =displacement /time
speed =distance/ time
and as we know displacement can be 0 but distance can't so,it's completely clear that average velocity can be 0 but average speed should not be 0.

hope it helps

Answer 2

This is because speed depends on distance and velocity upon displacement . we can have displacement 0 but distance can never be zero ,therefore average velocity can be zero but not average speed.