Chapter 4: Applications of Derivatives - Section 4.2 - The Mean Value Theorem - Exercises 4.2 - Page 198: 54

$48$ m/s.

Step 1. Given $a=1.6m/s^2$ and $v'=a$, we can write the general equation for the velocity as $v=at+C$ where $C$ is a constant. Step 2. The initial velocity of the rock is zero; we have $v(0)=0$ and $C=0$ Step 3. At $t=30$ sec, we have $v(30)=1.6\times30=48$ m/s.