Question

A rock is thrown vertically upward from the surface of an airless planet. It reaches a height of s = 120t - 4t2 meters in t seconds. How high does the rock go? How long does it take the rock to reach its highest point?

Answer 1

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 $s(t) = 120t - 4t^2$

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) = $120-8t$

This becomes 0 when t =15 seconds

Hence at 15th second the rock starts falling and upto

s(15) = $120(15)-4(15^2)\\= 900$ metres high it goes

The time taken to reach highest point is = 15 seconds.