Question

6. A body travels a distance of 10 km with a constant
speed of 30 km h- and then the next 40 km at a
constant speed of 50 km h-. Find the average speed
for the whole journey.​

Answer 1

Answer:

The average speed for the whole journey is 750/17 km/h

Explanation:

Given :

A body travels a distance of 10 km with a constant  speed of 30 km/h and then the next 40 km at a  constant speed of 50 km/h

To find :

the average speed for the whole journey

Solution :

• Speed = distance/time taken

Time taken to travel distance of 10 km :

speed = 30 km/h

distance = 10 km

time taken = distance/speed = 10/30 = 1/3 hr

Time taken to travel distance of 40 km :

speed = 50 km/h

distance = 40 km

time taken = distance/speed = 40/50 = 4/5 hr

• Average speed = total distance travelled/total time taken

 $\longrightarrow \sf Average \ speed =\dfrac{10+40}{\dfrac{1}{3}+\dfrac{4}{5}} \\\\ \implies \sf Average \ speed = \dfrac{50}{\dfrac{5+4(3)}{15}} \\\\ \implies \sf Average \ speed = \dfrac{50}{\dfrac{5+12}{15}} \\\\ \implies \sf Average \ speed = \dfrac{50}{\dfrac{17}{15}} \\\\ \implies \sf Average \ speed = 50 \times \dfrac{15}{17} \\\\ \implies \sf Average \ speed = \dfrac{750}{17} \ km/h$

Therefore, the average speed for the whole journey is 750/17 km/h