Chapter 8.5, Problem 46E

To determine

To find : The work Sampras had to do on the $2$ oz ball to get $124$ mph.

Answer to Problem 46E

The required word done is $64.6\text{ ft}\text{.lb}$

Explanation of Solution

Given information :

Weight of the ball is $2$ oz.

Speed is $124$ mph

Formula used :

Work done by force = change in K.E. $=\frac{1}{2}m{v}_2{}^2-\frac{1}{2}m{v}_1{}^2$

Calculation :

Here, $v_1=0$ and $v_2=124\text{ mph}=\frac{2728}{15}\text{ ft}/\sec$

Mass $\left(m\right)=\frac{2}{32\times 16}$ lb

Therefore, work done $=\frac{1}{2}m{v}_2{}^2-\frac{1}{2}m{v}_1{}^2$

  $\begin{array}{l}=\frac{1}{2}\times \frac{2}{32\times 16}\times {\left(\frac{2728}{15}\right)}^2\\ \approx 64.6\text{ ft}\text{.lb}\end{array}$