Question

A train moving at a constant velocity of $54km/hr$ moves eastwards for $30minutes,$ then due north with the same speed for $40minutes.$
What is the average velocity of the train during this run?

• A. $30$
• B. $35$
• C. $38.6$
• D. $49.3$

Answer 1

Answer: (C)

$38.6$

We know that

According to question distance east west $\to speed\times time$

$=54\times \frac{1}{2}hr$

$=27km$

distance north $\to 54\times \frac{40}{60}hr$

$=\frac{5}{4}\times \frac{2}{3}$

$=36km$.

Net distance $=\sqrt{(36{)}^2+(27{)}^2}$

$=45km$

Avg. velocity $=\frac{Totaldisplacement}{totaltime}=\frac{45}{(30+40/60)}$

$=\frac{45}{70/60}$

$=\frac{45\times 64}{76}=38.4$