Question

a train covers half of its journey at 10m/s and the other half at a speed of 15,m/s . The average speed of the train during the whole jorney is ?

Answer 1

12.5m per second
take the average of those two speeds

Answer 2

For the complete journey, the “average speed” of the train is 12 m/s  

Solution:

Let the total distance travelled by a train be 2S.

The as per the question the half distance that is “S” is travelled by speed 10 m/s.

Also the second half “S” is covered with a speed of 15 m/s.

So time taken = $\bold{\frac{\text { Distance }}{\text { Speed }}}$

$\Rightarrow \frac{S}{10}+\frac{S}{15}$

$=\frac{5 s}{30}$

$=\frac{s}{6}$

Speed$\bold{=\frac{\text {Distance}}{\text {Time}}}$

Total distance = 2S

Total time$=\frac{2 s}{\frac{s}{6}}$

Speed $=\frac{12 s}{s}$

= 12m/s  

12 m/s is the train’s average speed.