Chapter 2 - Kinematics: Description of Motion - Learning Path Questions and Exercises - Exercises - Page 60: 4

(a) Average speed, $s=0.5\,\mathrm{m/s}$. (b) Time taken at increase speed is $8.33\,\mathrm{min}$.

(a) Average speed, \begin{align*} s&=\frac{d}{t}=\frac{300}{10\times60}\\&=0.5\,\mathrm{m/s} \end{align*}(b) Increased speed, $s'=1.2\times0.5\,\mathrm{m/s}=0.6\,\mathrm{m/s}$ Time taken at this speed, \begin{align*} t'&=\frac{d}{s'}=\frac{300}{0.6}\\&=500\,\mathrm{s}\\&=8.33\,\mathrm{min} \end{align*}