Question

A car travels the first third half a distance with a speed half 10kmph the second third at 20kmph and the last third at60kmph what is its mean speed over the entire distance

Answer 1

Answer:

18km/h

Explanation:

Let the total distance travelled be x.

Let the total time taken be T.

Average speed = Total distance/Total time = x/T

First half,

v = 10 km/h

s = 1/3 x

t= x/3/10 = x/30

Second half,

v = 20 km/h

s = 1/3 x

t= x/3/20 = x/60

Third half,

v = 60 km/h

s = 1/3 x

t = x/3/60 = x/180

Now,

Time for entire journey, T = x/30 + x/60 + x/180

Or T = 6x + 3x + x/180

Or T= 10x/180

Or T = x/18

Now,

Average speed of the entire journey, Vav = Total distance/Total time

= x/x/18

= 18 km/h