If a flea jumps straight up, and if air resistance is neglected (a rather poor approximation in this situation), how high does the flea go?

Let say the Fly jumps in the air with speed speed vertically upwards

it will reach the highest point the final speed will become Zero

so here we can say that its uniform deceleration due to gravity of earth  

now by kinematics we can say

so above is the maximum height that will covered by the fly.

convex lenses are thicker at the middle. rays of light that pass through the lens are brought closer together (they converge). a convex lens is a converging lens. when parallel rays of light pass through a convex lens the refracted rays converge at one point called the principal focus.