Question

Two cars are moving in the same direction with a speed of $30\, km\, h^{-1}$. They are separated from each other by 5 km. Third car moving in the opposite direction meats the two cars after an interval of 4 min. What is the speed of the third car?

• A. $30\, km\, h^{-1}$
• B. $35\, km\, h^{-1}$
• C. $40\, km\, h^{-1}$
• D. $45\, km\, h^{-1}$

Answer 1

Answer: (D)

Let speed of the third car be $ \upsilon \,km\,h^{-1}$
Then, relative speed of third car with respect to two cars
$= \left(\upsilon + 30 \right) \,km\,h^{-1}$
Two cars are separated by 5 km and third car crosses them in 4 min.
$\therefore \quad\upsilon + 30 = \frac{5\times60}{4} = 75 \Rightarrow \upsilon = 75-30 = 45\,km\,h^{-1}$