2 The driver of a car slams on the brakes when he sees a tree blocking
3 the road. The car slows uniformly with an acceleration of
4 $-5.60\U{m/s$^2$}$ for $4.20\U{s}$, making straight skid marks
5 $62.4\U{m}$ long, all the way to the tree. With what speed does the
6 car then strike the tree?
10 The speed of the car is given by
14 and its position is given by
16 x(t) = \frac{1}{2} a t^2 + v_0 t + x_0
19 We know $a$, $t$, and $x-x_0$, so we can use the second equation to
22 v_0 = \frac{x-x_0-\frac{1}{2}at^2}{t}
24 We can plug this into the first equation to find the final velocity.
26 v &= at + \frac{x-x_0-\frac{1}{2}at^2}{t} \\
27 &= -5.60\U{m/s$^2$} \cdot 4.20\U{s}
28 +\frac{62.4\U{m} - \frac{1}{2}\cdot(-5.60\U{m/s$^2$})\cdot(4.20\U{s})^2}