Chapter 4.8, Problem 18P

To determine

To find how long was the apple in the air ?

Answer to Problem 18P

For 2.5 seconds the apple was in the air.

Explanation of Solution

Given information: A Balcony 40ft above him, he tossed it upward with an initial speed of 56ft/s.

Calculation: The required solution is obtained as,

Use the projectile equation, $h=vt-16t^2$ .

Velocity , $v=56ft/s$

Height , $h=40ft$

  $\begin{array}{l}h=vt-16t^2\\ 40=56t-16t^2\\ 16t^2-56t+40=0\\ 2t^2-7t+5=0\\ \left(2t-5\right)\left(t-1\right)=0\\ t=1,2.5\end{array}$

At $t=2.5$ seconds, 2.5 seconds after it was thrown, the apple passes kim on the balcony and she catches it. The time the apple was in the air was 2.5 seconds.

Hence, for 2.5 seconds the apple was in the air.