Question

a long distance runner Travels first 10 km at a uniform speed of 10 km per hour the next 20 km with the uniform speed of 5 km per hour and the last 10 km with the uniform speed of 10 km per hour find his average speed for the entire race

Answer 1

You can do this with that method

Answer 2

Answer:

Average speed, V = 6.66 km/h

Explanation:

It is given that,

A long distance runner Travels first 10 km at a uniform speed of 10 km per hour,

d₁ = 10 km

v₁ = 10 km/h

Next 20 km with the uniform speed of 5 km per hour,

d₂ = 20 km

v₂ = 5 km/h

The last 10 km with the uniform speed of 10 km per hour,

d₃ = 10 km

v₃ = 10 km/h

So, total distance covered is, d = d₁ + d₂ + d₃

d = 40 km

Total time taken, $t=\dfrac{d_1}{v_1}+\dfrac{d_2}{v_2}+\dfrac{d_3}{v_3}$

$t=\dfrac{10}{10}+\dfrac{20}{5}+\dfrac{10}{10}=6\ h$

Average speed for the entire race is calculated as :

$Average\ speed=\dfrac{total\ distance}{total\ time}$

$V=\dfrac{40\ km}{6\ h}=6.66\ km/h$

So, the average speed for the entire race is 6.66 km/h. Hence, this is the required solution.