Question

A rock is thrown vertically upward from the surface of an airless planet. It reaches a height of s = 120t - 6t^2 meters in t seconds. How high does the rock go? How long does it take the rock to reach its highest point?1190 m, 10 sec600 m, 10 sec1200 m, 20 sec2280 m, 20 sec

Answer 1

$\begin{gathered} \text{Given} \\ s=120t-6t^2 \end{gathered}$

Substitute t = 10, and t = 20, to the given equation and we get

$\begin{gathered} \text{If }t=10 \\ s=120t-6t^2 \\ s=120(10)-6(10)^2 \\ s=1200-6(100) \\ s=1200-600 \\ s=600 \\ \\ \text{If }t=20 \\ s=120t-6t^{2} \\ s=120(20)-6(20)^2 \\ s=2400-6(400)^2 \\ s=2400-2400 \\ s=0 \end{gathered}$

We therefore have t = 10 as the time it takes to reach the highest point, with the rock reaching 600m.

Therefore, we choose second option.