To solve the problem, we can use the information given about the rock's fall:
- The rock falls for a total time of 3 seconds.
- Its final velocity just before hitting the ground is 29.4 m/s.
Using the equation of motion relating final velocity (\(v\)), initial velocity (\(u\)), acceleration (\(a\)), and time (\(t\)):
\[ v = u + at \]
Assuming the rock starts from rest, the initial velocity \(u = 0\). Thus, the equation simplifies to:
\[ v = at \]
Substituting the values we have:
\[ 29.4 , \text{m/s} = a \cdot 3 , \text{s} \]
To solve for \(a\), divide both sides by 3 seconds:
\[ a = \frac{29.4 , \text{m/s}}{3 , \text{s}} = 9.8 , \text{m/s}^2 \]
Thus, the acceleration of the rock in the downward direction is:
C. 9.8 m/s²