Chapter 9.1, Problem 12SSC

To determine

To Explain: The reason for bending the knees while jumping from a height to the ground.

Explanation of Solution

Introduction:

From Newton’s second law

  $F=ma$

Now, the definition of momentum

  $p=mv$

Acceleration $a=\frac{\Delta v}{\Delta t}$

Then from Newton’s second law

  $\begin{array}{l}F=m\left(\frac{\Delta v}{\Delta t}\right)\\ F=\frac{\Delta \left(mv\right)}{\Delta t}\end{array}$

Here, mass $m$ is constant quantity for body.

Therefore, replacing the by momentum then net force become

  $F_{net}=\frac{\Delta p}{\Delta t}$

The force equals the momentum divided by time. If there is larger time, then net force ( $F_{net}$ ) decreases (inverse relation).So, by bending knees as onehits the floor,one increases the time of the entire incident leading to a decreased net force $F_{net}$ experienced bythe body.