Question

a car is moving on a straight Road covers one third of the distance with a speed of 20km/h and the rest with the speed of 60km/h. the average speed of the car​

Answer 1

☆Solution ☆

Let the distnace travelled by a car on staright path  be x.

The one thrid distance is covered with speed of 20 km/h and the rest two- third distance with speed of 60 km/h

Thus, 

time required for the one third of the journey is 

$\frac{x \: is \: to \: 3}{20} = \frac{x}{60}$

The time required for the next part of the journey is

$\frac{2x \: is \: to \: 3}{60} = \frac{x}{90}$

Thus the total time taken to complete the journey is

$\frac{x}{60} + \frac{x}{90} = \frac{x}{36}$

Thus the Average speed is ,

Average speed = Total distance travelled / total time taken

Average speed

$= > \frac{x}{x \: is \: to \: 36}$

Thus, the average speed = 36km/h

Answer 2

Answer:

Average speed = 36m/s

Explanation:

We know that ,

Speed = distance/ time

$20 = \frac{ \frac{x}{3} }{t _{1}} \\ \implies t_{1} = \frac{x}{60}$

And ,

$60 = \frac{ \frac{2}{3}x }{t _{2} } \\ \implies t_{2} = \frac{2}{3 \times 60} x \\ \implies t_{2} = \frac{x}{90}$

Now considering the whole path

$average \: speed \: = \frac{x}{t _{1} + t_{2} } \\ \implies \: s = \frac{x}{ \frac{x}{60} + \frac{x}{90} } \\ \implies \: s \: = \frac{x}{ \frac{3x + 2x}{180} } \\ \implies \:s = \frac{180x}{5x} \\ \implies \: s = 36m {s}^{ - 1}$

Therefore , the average speed is 36 m/s