Question

a rock falls off a cliff and hits the ground after three seconds. the rocks velocity is 29.4 m/s when it hits the ground. what is its acceleration of the rock in the downward direction? 0.31 m/s² 3 m/s² 9.8 m/s² 88.2 m/s²

Explanation:

Step1: Recall the formula for acceleration

The formula for acceleration \(a=\frac{v - u}{t}\), where \(v\) is final velocity, \(u\) is initial velocity, and \(t\) is time.
For a rock falling off a cliff, the initial velocity \(u = 0\ m/s\) (starts from rest).

Step2: Substitute the values into the formula

Given \(v=29.4\ m/s\), \(u = 0\ m/s\), and \(t = 3\ s\).

$$a=\frac{29.4- 0}{3}$$

$$a = 9.8\ m/s^{2}$$

Answer:

\(9.8\ \frac{m}{s^{2}}\) (the third option)