$12-122.$ If the car passes point A with a speed of $20\frac{m}{s}$ and begins to increase its speed at a constant rate of $a_t=0\mathrm{.}5\frac{m}{s^2},$ determine the magnitude of the car's acceleration when $s=101\mathrm{.}68m$ and $x=0.$ Ans: $a=1\mathrm{.}68\frac{m}{s^2}$