Question

Suppose you drive to Delhi ($200km$ away) at $400km/hr$ and return at $200km/hr$. What is yours average speed for the entire trip?

• A. Zero
• B. $300Km/hr$
• C. Less than $300km/hr$
• D. More than $300km/hr$

Answer 1

Answer: (C)

Average speed $=\frac{\text{ Total Distance }}{\text{ Total Time }}$
$=\frac{d_1+d_2}{t_1+t_2}$
$=\frac{200+200}{\frac{200}{400}+\frac{200}{200}}$
$[\because t_1=\frac{d_1}{v_1}$ and $t_2=\frac{d_2}{v_2}]$
$=\frac{400}{\frac{1}{2}+1}$
$=\frac{400}{\frac{1+2}{2}}=\frac{800}{3}=266.66\simeq 267km/h$
i.e.it is less than $300km/h$.