A particle travels first half of the total time with speed `v_1` and second half time with speed `v_2.` Find the average speed during the complete journey.

Explanation

`s_(1)=v_(1)t` and `s_(2)=v_(2)t`
Total distance `=s_(1)+s_(2)=(v_(1)+v_(2))t`
Total time `=t+t=2t` then `v_("avg.")=(s_(1)+s_(2))/(t+t)=((v_(1)+v_(2))t)/(2t)=(v_(1)+v_(2))/(2)`