Question

Two cars are moving in the same direction with the same speed $30km/hr$. They are separated by a distance of $5km$ the speed of a car moving in the opposite direction if it meets these two cars at interval of 4 minutes, will be:

• A. $40km/hr$
• B. $45km/hr$
• C. $30km/hr$
• D. $15km/hr$

Answer 1

The correct option is B $45km/hr$

This is related to relative motion,

Let the two cars moving in the same direction be A and B and the third car be C.

Let the velocity of C be 'u'.

So the velocity of C with respect to B would be. $u+30$(as they are moving in opposite directions).

Do the speed $u+30$ would be given by:

$=\frac{5}{\left(\frac{4}{60}\right)}=u+30$

$\Rightarrow 5\times \frac{60}{4}=u+30\Rightarrow 75=u+30$

Hence $u=45kmph$