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larisa86 [58]
3 years ago
6

A biker goes up hill with a constant speed of 10km/h. Then he goes downhill with a constant speed of 50km/h. What's his average

speed
Physics
1 answer:
Sladkaya [172]3 years ago
4 0

This is not as simple as it looks.  

His average speed is NOT (10km/hr + 50km/hr)/2 = 30 km/hr.

You have to use the definition of speed:

Speed = (total distance covered) / (time to cover the distance).

Let's say the distance up (and down) the hill is 'd' .

Then the time it takes to go up the hill is (d/10) hours.

And the time it takes to come down the hill is (d/50) hours.

Total distance = 2d km

Total time = (d/10) + (d/50) = (5d/50) + (d/50) = 6d/50

Speed = distance/time = 2d/(6d/50) = 100d/6d

<em>Speed = </em>100/6 = <em>16-2/3 km/hr</em>

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