Question

A motorcyclist drives from place A to B with a uniform speed of
10 km h–1 and returns from place B to Awith a uniform speed of
20 km h–1. Find his average speed.

Answer 1

Explanation:

average speed = 2v1v2/v1 + v2

given, v1=10kmph,v2 = 20 kmph

average speed = 2(10)(20)/10 + 20

=400/30

=13.33 kmph

Answer 2

Given:

Speed of motorcyclist while driving from A to B,v₁= 10 km/h

Speed of motorcyclist while driving from B to A,v₂= 20 km/h

To Find:

Average speed of motorcyclist

Solution:

We know that,

• If a body covers first half of a distance with speed v₁ and second half with speed v₂, then average speed of body S is given by,

$\pink{\underline{\boxed{\bf{S=\dfrac{2v_{1}v_{2}}{v_{1}+v_{2}}}}}}$

$\rule{190}{1}$

Since, distance covered by motorcycle in going and returning is same, so both the path can be considered as half of whole journey.

Let the average speed of car be S

So,

$\longrightarrow\rm{S=\dfrac{2v_{1}v_{2}}{v_{1}+v_{2}}}$

$\longrightarrow\rm{S=\dfrac{2\times10\times20}{10+20}}$

$\longrightarrow\rm{S=\dfrac{400}{30}}$

$\longrightarrow\rm{S=13.33\ km/h}$

Hence, the average speed of motorcyclist is 13.33 km/h.