Question

A vehicle travels half or the total distance with speed $36km/h$ and next half with $54km/h$. The average speed is

• A. $12m{s}^{-1}$
• B. $12.5m{s}^{-1}$
• C. $43.2km/h$
• D. $7.5m{s}^{-1}$

Answer 1

The correct option is C $43.2km/h$

average speed = total distance / total time

$=\frac{s_1+s_2}{t_1+t_2}$

$=\frac{x+x}{\frac{x}{36}+\frac{x}{54}}$

$=\frac{2x}{x(\frac{1}{36}+\frac{1}{54})}$

$=\frac{2}{\left(\frac{5}{108}\right)}$

$=\frac{216}{5}=43.2km/h$