Chapter 7.5, Problem 44E

To determine

To find: The work done in throwing a baseball at the speed of $40\text{m/sec}$ .

Answer to Problem 44E

  $114\cdot 4\text{joule}$

Explanation of Solution

Given information:

How many joules of work does it take to throw a baseball $40\text{m/sec}\left(\text{about}\text{90mph}\right)$ . A baseball has a mass of $143g$ .

The Kinetic Energy of the moving baseball is given by:

  $K=\frac{1}{2}m{v}^2$

  $m$ is the mass of the baseball and $v$ is the velocity of the moving ball.

  $m=143\text{g=}\frac{143}{\text{1000}}\text{kg=0}\text{.143}\text{kg}$

Substitute $m=\text{0}\text{.143}\text{kg}$ and $v=40\text{m/s}$ into the formula of Kinetic Energy

  $\begin{array}{l}K=\frac{1}{2}\times 0.143\times {\left(40\right)}^2\\ =\frac{1}{2}\times 0.143\times 1600\\ =114\cdot 4\text{joule}\end{array}$

The work done by Force in moving the baseball equals the Kinetic Energy.

Hence, the work done to move the baseball at the desired speed is $114\cdot 4\text{joule}$ .