A ball is thrown straight upward from ground level with a speed of 18 m/s. How much time passes before the ball strikes the ground if we disregard air resistance?
A) 1.8 s
B) 0.6 s
C) 3.7 s
D) 1.1 s

Question

Quizplus · Accepted Answer

To solve this problem, we use the equation of motion under constant acceleration due to gravity (g = 9.8 m/s^2). The time (t) it takes for the ball to reach its highest point can be found using the formula $v = u + at$, where $v$ is the final velocity (0 m/s at the highest point), $u$ is the initial velocity (18 m/s), and $a$ is the acceleration (-9.8 m/s^2, since it's acting opposite to the direction of motion). Solving for $t$, we get $t = \frac{v - u}{a} = \frac{0 - 18}{-9.8} = 1.84$ seconds to reach the highest point. The total time for the journey up and down is twice this, since the time to ascend and descend are the same when air resistance is ignored, giving $2 \times 1.84 = 3.68$ seconds, which rounds to $3.7$ seconds.

A Ball Is Thrown Straight Upward from Ground Level with a Speed