Question

A car moves with a speed of 30 km/h–1 for half an hour, 25 km/h–1 for one hour and 40 km/h–1 for two hours. Calculate the average speed of the car.

Answer 1

30km/hr = s×t = 30×1/2=15km.

25km/hr= s×t= 25×1 =25km.

40km/hr=s×t= 40×2=80km

Therefore, total distance overed= 15+25+80=120km

Total time taken= 3hrs and 30 mins=7/2 hrs.

Therefore, average speed=total distance covered/total time taken = 120×2/7 = 34.28km/hr

Answer 2

$\sf\huge{\boxed{\underline{Question}}}$

▶A car moves with a speed of 30 km/h–1 for half an hour, 25 km/h–1 for one hour and 40 km/h–1 for two hours. Calculate the average speed of the car.

$\sf\huge\bold{\boxed{\underline{Answer}}}$

Given▶

let v1 , v2,v3 be the respective speeds covering distances s1,s2,s3 in time interval t1,t2,t3.

we have,

s1 = $v1\times t1$

s1 = $30\times \frac{1}{2}$

s1 = 15km

________

s2 =$v2\times t2$

= $25\times 1$

= 25km

___________

s3 = $v3\times t3$

= $40\times 2$

= 80km

__________

we have Average speed is equal to!

V(av) = $\frac{s1+s2+s3}{t1+t2+t3}$

= $\frac{15+25+80}{\frac{1}{2}+1+2}$

= $\frac{120}{\frac{1+2+4}{2}}$

= $\frac{120\times 2}{7}$

=$\frac{240}{7}$

= 34.28km\h