Question

if a ball is thrown up at 30 m/s at the edge of a cliff, what is the velocity 5 s later? (assume no air resistance)
-10 m/s
-20 m/s
-30 m/s
-50 m/s

Explanation:

Step1: Identify the kinematic - equation

We use the equation $v = v_0+at$. Here, $v_0$ is the initial velocity, $a$ is the acceleration, and $t$ is the time.

Step2: Determine the values of variables

The initial velocity $v_0 = 30$ m/s (upward, positive), the acceleration $a=-g=- 10$ m/s² (downward, negative, where $g$ is acceleration due to gravity), and $t = 5$ s.

Step3: Substitute values into the equation

$v=v_0 + at=30+( - 10)\times5$.
$v=30 - 50=-20$ m/s.

Answer:

B. -20 m/s