a boy runs for 10 min at a uniform speed of 9 km/h. at what speed should he run for the next 20 min. so that the average speed comes 12km/hr
Answers
Answered by
37
Distance covered in 10 minutes = 9 kmph * 10/60 hrs = 1.5 km
Speed for the 2nd leg = V kmph
Distance coveed in 2nd leg = V * 20/60 = V / 3 km
Overall average speed = total distance / total time =
( 1.5 + V/3 ) / (10+20)/60 = 12 km ph
2 (1.5 + V/3) = 12
1.5 + V/3 = 6
V = 13.5 KMPH
Speed for the 2nd leg = V kmph
Distance coveed in 2nd leg = V * 20/60 = V / 3 km
Overall average speed = total distance / total time =
( 1.5 + V/3 ) / (10+20)/60 = 12 km ph
2 (1.5 + V/3) = 12
1.5 + V/3 = 6
V = 13.5 KMPH
Answered by
20
so t = 60 min=1/6 hr
speed = 9 km/h
displacement = 9 x 1/6 = 1.5 km
again
let speed = X km/h
time = 20 min = 20 / 60 = 1/3 hr
displacement = X x 1/3 = X/3
so av. velocity = total displacement /time taken
=
(15/10 +X/3)/(1/2) = 12
⇒x = 13.5 km
speed = 9 km/h
displacement = 9 x 1/6 = 1.5 km
again
let speed = X km/h
time = 20 min = 20 / 60 = 1/3 hr
displacement = X x 1/3 = X/3
so av. velocity = total displacement /time taken
=
(15/10 +X/3)/(1/2) = 12
⇒x = 13.5 km
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