Solve the problem. Round your answer to the nearest tenth, when appropriate.
-A rock falls from a tower that is $78.4 \mathrm{~m}$ high. As it is falling, its height is given by the formula $\mathrm{h}=78.4-4.9 \mathrm{t}^{2}$. How many seconds will it take for the rock to hit the ground $(\mathrm{h}=0)$ ?
A) $8.9 \mathrm{sec}$
B) $1254.4 \mathrm{sec}$
C) $8.6 \mathrm{sec}$
D) $4 \mathrm{sec}$

Question

Quizplus · Accepted Answer

To find the time it takes for the rock to hit the ground, set $h = 0$ and solve for $t$:  $0 = 78.4 - 4.9t^2$  $4.9t^2 = 78.4$  $t^2 = 16$  $t = 4$ seconds.

Solve the Problem 78.4 m78.4 \mathrm{~m}78.4 m High as It Is Falling, Its Height Is Given by When

Solve the Problem $78.4 \mathrm{~m}$ High as It Is Falling, Its Height Is Given by When