Question

After a model rocket reached its maximum height, it then took 5.0 seconds to return to the launch site. what is the approximate maximum height reached by the rocket? [neglect air resistance.]

Answer 1

Air resistance is ignored.
g = 9.8 m/s².
At maximum height, the vertical velocity is zero.

Let h =  the maximum height reached.
Let u =  the vertical launch velocity.

Because ot takes 5.0 seconds to reach maximum height, therefore
(u m/s) - (9.8 m/s²)*(5 s) = 0 
u = 49 m/s

The maximum height reached is
h = (49 m/s)*(5 s) - (1/2)*(9.8 m/s²)*(5 s)²
   = 122.5 m

Answer: 122.5 m