Question

A car moving on a straight road covers the half of thetotal distance with 36 km/h and the rest with 54 km/h ,the average speed of car is
O 9 m/s
O 12 m/s
O 27 m/s
O 18 m/s​

Answer 1

Given:

A car moving on a straight road covers the half of the total distance with 36 km/h and the rest with 54 km/hr.

To find:

Average speed of car?

Calculation:

Let average speed be v :

$v = \dfrac{total \: distance}{total \: time}$

$\implies v = \dfrac{2d}{ \dfrac{d}{36} + \dfrac{d}{54} }$

$\implies v = \dfrac{2}{ \dfrac{1}{36} + \dfrac{1}{54} }$

$\implies v = \dfrac{2}{ \dfrac{3 + 2}{108} }$

$\implies v = \dfrac{2 \times 108}{ 5 }$

$\implies v = 43.2 \: km/hr$

$\implies v = 43.2 \times \dfrac{5}{18} \: m/s$

$\implies v = 12\: m/s$

So, average speed is 12 m/s.