What is the maximum height?

Question

An object is launched upward with an initial velocity of 64 ft per second from a platform 80 ft high.

Answer 1

Use S=ut-gt²/2 where S is vertical height, u=64’/s, t is the time in secs, g=9.8’/s², accn of gravity.

Differentiate this wrt t: u=gt, t=u/g=64/9.8=6.53 secs to reach maximum height.

S=u²/g-g(u/g)²/2=u²/2g=2048/9.8=208.98 ft. This is from the level of the platform, so from the ground it is 288.98 ft.