A grenade flies out of the cannon at a speed of 
at an angle 
relative to the horizontal ground. The time t of the grenade is described by the equation 
, where the gravitational acceleration on the Earth's surface is 
.
a) What is the maximum height reached by a grenade? In what time does the grenade reach its maximum height?
b) How long do we have to set the grenade to explode at a height of five meters?
with a maximum height 
.
when it reaches a height 
when lifting upwards, or to a time 
when it will be at this height when falling downwards.
