Answer:
Step-by-step explanation:
Given that a rock is thrown vertically upward from the surface of an airless planet. It reaches a height of [tex]s(t) = 120t - 4t^2[/tex]
where t is expressed in seconds
The rock goes upto a height where the velocity becomes 0 and then it starts falling down by gravity
Velocity at time t = s'(t) = [tex]120-8t[/tex]
This becomes 0 when t =15 seconds
Hence at 15th second the rock starts falling and upto
s(15) = [tex]120(15)-4(15^2)\\= 900[/tex] metres high it goes
The time taken to reach highest point is = 15 seconds.
