Question

A car travels 30 km at a uniform speed of 40km/h and the next 30 km at a uniform speed of 20km/h. Find its average speed.

Answer 1

Heya Mate.............

Here is your solution..................

Given that ,

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 ( answer )  

@Rajasthani............

Answer 2

$\huge\mathfrak{A{\underline{\underline{\textbf{\red{nswer :}}}}}}$


Average Speed = ?

$D_{1}$ (Distance) = 30 km

$S_{1}$ (Speed) = 40 km/hr.

$t_{1}$ (time) = $\dfrac{D1}{S1}$

$\dfrac{30}{40}$ => $\dfrac{3}{4}$

Similarly...

$D_{2}$ (Distance) = 30 km

$S_{2}$ (Speed) = 20 km/hr.

$t_{2}$ (time) = $\dfrac{D2}{S2}$

$\dfrac{30}{20}$ => $\dfrac{3}{2}$

Now... total time = $t_{1}$ + $t_{2}$

= $\dfrac{3}{4}\:+\:\dfrac{3}{2}$

= $\dfrac{6\:+\:3}{4}$

= $\dfrac{9}{4}$

= 2.25 hr.

Total distance = $D_{1}$ + $D_{2}$

= 30 + 30 = 60 km

Now..

Average Speed = $\dfrac{Total\: Distance}{Total\: time}$

= $\dfrac{60}{2.25}$

= 26.66 km/hr

$\boxed{\boxed{\textbf{Average Speed = 26.6 km/hr.}}}$

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