Question

A car travels half of the length of straight line motion speed of 60 km per hour and the remaining part of the distance is covered with a speed 40 km per hour for half of the time of remaining journey and with speed 20 km per hour for other half of the time. the average speed of the car is ​

Answer 1

Explanation:

answer is 40 km/hr

hope it's the correct answer

Answer 2

Given that,

The car covered half of length of straight with speed of 60 km/hr.

The car covered remaining half length of straight with 40 km/hr in half of time and with 20 km/hr for other half of time.

Suppose the total distance is 2x km.

Time taken in traveling the first distance x will be

$t_{1}=\dfrac{x}{v_{1}}$

Put the value into the formula

$t_{1}=\dfrac{x}{60}$....(I)

Time taken of half length of straight line is

$t_{2}=t+t'$

$t_{2}=\dfrac{x}{2\times v}+\dfrac{x}{2\times v'}$

Put the value into the formula

$t_{2}=\dfrac{x}{2\times40}+\dfrac{x}{2\times20}$

$t_{2}=\dfrac{x}{80}+\dfrac{x}{40}$

We need to calculate the average speed of the car

Using formula of average speed

$v_{avg}=\dfrac{D}{T}$

Where, D = total distance

T = total time

$v_{avg}=\dfrac{2x}{t_{1}+t_{2}}$

$v_{avg}=\dfrac{2x}{t_{1}+t+t'}$

Here, $t_{2}=t+t'$

Put the value into the formula

$v_{avg}=\dfrac{2x}{\dfrac{x}{60}+\dfrac{x}{80}+\dfrac{x}{40}}$

$v_{avg}=\dfrac{2}{\dfrac{1}{60}+\dfrac{1}{80}+\dfrac{1}{40}}$

$v_{avg}= 36.9\ km/h$

Hence, The average speed of the car is 36.9 km/hr.