A body is projected vertically upward with an initial velocity u. If acceleration due to gravity is g, time for which it remains in air is:
2ug
When body reaches highest point, final velocity, v=0
Let the time required to reach highest point be t1
Using equation of motion:
v=u+at, we get
v=u−gt1 [as a=−g]
⇒0=u−gt1
⇒gt1=u
⇒t1=ug
Time taken by the body to reach the highest point = time taken by body to come back to the initial point after reaching the highest point.
Therefore,
Total time=2×Time taken to reach highest point
Hence, total time =2ug