The bullet is fired vertically upwards and returns to the ground in 20 s. The maximum height reached by the bullet has to be determined.
Let the velocity with which the bullet is fired be X. There is a downward acceleration acting on the bullet equal to 9.8 m/s^2. At the highest point the vertical velocity of the bullet is 0.
V - 9.8*t = 0
=> V = 9.8*t
The time taken by the bullet to go up is the same as the time taken by it to come down.
t = 10 s
V = 98 m/s
The distance traveled in 10 s is s = 98*10 - (1/2)*9.8*100
=> 980 - 490
=> 490 m
The maximum height of the bullet is 490 m.