Question

Consider a truck contains many birds sitting in it.if the birds started flying,does it lighten the truck?

Answer 1

the mass of the truck will be the same.
no matter what the birds are doing inside it.
when the birds starts flying, they will need to produce equal force on air to cancel gravity. so the truck will not lighten

Answer 2

the mass of the truck will be the same.

no matter what the birds are doing inside it.

when the birds starts flying, they will need to produce equal force on air to cancel gravity. so the truck will not lighten