A cyclist and his bicycle have a total mass of $81{\text{ }}kg$. The cyclist starts from rest and rides in a straight line. The cyclist exerts a constant force of $135{\text{ }}N$ and the motion is opposed by a resistance of magnitude $9v{\text{ }}N$, where $vm{\text{ }}{s^{ - 1}}$ is the cyclist’s speed at time $t\,s$ after starting.
a) Show that $\frac{9}{{15 - v}}\frac{{dv}}{{dt}} = 1$.
b) Solve this differential equation to show that $v = 15\left( {1 - {e^{ - \frac{1}{9}t}}} \right)$.
c) Find the distance travelled by the cyclist in the first 9 s of the motion.
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