Question

Travelling on a National Highway it travels 30 km at a uniform speed of 40 km per hour and the next 30 km at a uniform speed of 20 km per hour find its average speed.

Answer 1

Given:-

Firstly it cover 30km at a uniform speed of 40 km/hr.

Secondly it cover 30 km at a uniform speed of 20km/hr

To Find:-

Average speed =?

Solution:-

Total distance covered by the car = (30 +30 )= 60 km.

The t taken to cover first 30 km,

$\sf t = \frac{30}{40} h = \frac{3}{4} h$

The t taken to cover next 30 km,

$\sf t = \frac{30}{20}h = \frac{3}{2} h$

So, the total time taken = t1 + t2 =

$\sf( \frac{3}{4} + \frac{3}{2} )h = \frac{9}{4} h$

we have , average speed =

$\sf \frac{total \: distance \: covered}{total \: time} = \frac{ \frac{60}{9} }{4} \frac{km}{h} = \frac{60 \times 4}{9} \frac{km}{h} = 36.7 \frac{km}{h}$

Answer 2

Answer:

Explanation:

 1st 30 km uniform speed is (u1) = 40 km/h  

    2nd 30 km uniform speed is ( u2 ) = 20 km/h

    total distance ( d ) = 30 + 30 = 60 km

    time taken in 1st time = d / t = 30/40 also, 3h / 4 = 180/4 = 45 min

    time taken in 2nd time = d/t = 30/20 also, 3h/2 = 180/2 = 90 min

   total time = 45 + 90 = 135 min = 135/60 h

av.speed = 60/135/60 = 60 * 60 /135 = 26.66 km/h

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