Chapter 4, Problem 72GP

To determine

To find: The average force of air resistance.

Answer to Problem 72GP

  $F_R=4.3N$

Explanation of Solution

Given Data:

Mass of purse $(\text{m})=2\text{kg}$

Height through which it falls (h) $=55\text{m}$

Initial speed of purse $\left(v_0\right)=0$

Formula Used:

  $v^2-v_0^2=2a(s)$

  $mg-F_R=ma$

Calculation:

The down ward acceleration is determined using

  $\begin{array}{l}{v}^2-v_0^2=2a(s)\hfill \\ {29}^2-0=2\times a\times 55\hfill \\ a=\frac{{29}^2}{2\times 55}\hfill \\ a=7.64\text{m}/{\text{s}}^2\hfill \end{array}$

The forces acting on the purse are the gravity acting downwards and the air resistance acting

upwards.

Applying 's II Law,

  $\begin{array}{l}mg-F_R=ma\\ \begin{array}{l}{F}_R=m(g-a)\hfill \\ =2(9.8-7.64)\hfill \\ =4.3N\hfill \\ F_R=4.3N\hfill \end{array}\end{array}$

Conclusion:

The average force of air resistance is $F_R=4.3N$ .