\begin{problem*}{8.6}
A friend claims that as long as he has his seat belt on, he can hold
on to an $m = 12.0\U{kg}$ child in a $v_i = 60.0\U{mph}$ head-on
collision with a brick wall in which the car passenger compartment
comes to a stop in $\Delta t = 0.050\U{s}$.  Show that the violent
force during the collision will tear the child from his arms.
\end{problem*}

\begin{solution}
The force needed to hold on to the child is given by
\begin{equation}
 F = \frac{\Delta p}{\Delta t} = - m \frac{v_i}{\Delta t}
   = -12.0\U{kg}\frac{60\U{mph}}{0.050\U{s}}
     \cdot \frac{1609\U{m}}{1\U{mi}} \cdot \frac{1\U{hr}}{3600\U{s}}
   = -6436\U{N}
\end{equation}
Which is much larger than what the friend is capable of applying.
\end{solution}
