Question

Bob has covered some distance with a speed of 50 km/hr in 2 hrs. And then some more distance in another 2 hrs, with a speed of 40 km/hr. Find the average speed for his entire journey.

• A. 90 km/hr
• B. 45 km/hr
• C. 90 m/s
• D. 45 m/s

Answer 1

The correct option is B

45 km/hr

Here, since the time of travel is constant, Average speed = $\frac{S1+S2}{2}$ , where S1, S2 ------ given two speeds

That is, $\frac{50+40}{2}=45km/hr$

So, Average speed = 45 km/hr

Aliter:-

We have known that Average speed =$\frac{Totaldistancecovered}{Totaltimetaken}$

ie, Total distance=( 50 km/hr in 2 hrs = 100 km) + (40 km/hr in 2 hrs = 80 km) = 180 km

And, Total time taken = 2 hrs + 2 hrs = 4 hrs

So, Average speed = 180 /4 = 45 km/hr