Chapter 4, Problem 80GP

To determine

To find: The net horizontal force F that the straps of the restraint chair must exert on the child in order to keep her fixed to the chair.

Answer to Problem 80GP

  $\begin{array}{l}F=-750\text{N}\hfill \end{array}$

Explanation of Solution

Given Data:

Mass of child $=12\text{kg}$

Initial speed of car

  $\begin{array}{l}\left(v_0\right)=45\text{km}/\text{hr}\\ =12.5\text{m}/\text{s}\end{array}$

Collision time $(t)=0.20$ secs

Formula Used:

  $v=u+at$

  $F=m\times a$

Calculation:

Let’s find the acceleration of the car from

  $\begin{array}{l}v=u+at\\ 0=12.5+a\times 0.20\\ a=-62.5\text{m}/{\text{s}}^2\end{array}$

The net horizontal force that the straps of the chair must exert on the child

  $\begin{array}{l}F=m\times a\\ F=12\times (-62.5)\\ =-750\text{N}\end{array}$

Conclusion:

The force of straps $\begin{array}{l}F=-750\text{N}\hfill \end{array}$ opposite to the velocity.