Question

4. A person travels a total distance of 360 km by a car. He covers the first half at a speed o
60 km h-' and the other half at 45 km hl. Find:
(a) the total time taken to complete the entire journey.
(b) average speed of the car.​

Answer 1

ANSWER:

• (a) The total time taken to complete the entire journey = 7 hrs.

• (b) Average speed of the car = 51.43 kmph.

GIVEN:

• A person travels a total distance of 360 km by a car.

• He covers the first half at a speed of 60 kmph.

• The other half at at a speed of 45 kmph.

TO FIND:

• (a) The total time taken to complete the entire journey.

• (b) Average speed of the car.

EXPLANATION:

$\boxed{\bold{\large{\gray{Time = \dfrac{Distance}{Speed}}}}}$

$\sf Total\ time = t_1 + t_2$

$\sf t_1 = \dfrac{\dfrac{360}{2}}{s_1}$

$\sf t_2 = \dfrac{\dfrac{360}{2}}{s_2}$

$\sf Total\ time = \dfrac{360}{2} \left( \dfrac{1}{s_1} + \dfrac{1}{s_2} \right)$

$\sf s_1 = 60\ kmph$

$\sf s_2 = 45\ kmph$

$\sf Total\ time = 180 \left( \dfrac{1}{60} + \dfrac{1}{45} \right)$

$\sf Total\ time = \dfrac{180}{15} \left( \dfrac{1}{4} + \dfrac{1}{3} \right)$

$\sf Total\ time = 12 \left( \dfrac{3 + 4}{12} \right)$

$\sf Total\ time = 7 \ hrs$

$\boxed{\bold{\large{\gray{Avg\ speed = \dfrac{Total \ distance}{Total \ time}}}}}$

$\sf Total \ distance=360\ km$

$\sf Total \ time= 7\ hrs$

$\sf Avg\ speed = \dfrac{360}{7}$

$\sf Avg\ speed =51.43 \ kmph$

Hence the total time taken to complete the entire journey is 7 hrs and the average speed of the car is 51.43 kmph.

Answer 2

a). the total time taken to complete the entire journey =7 hrs

b). average speed of the car = 51.43 kmph