Question

on a 60km track a train travels the first 30km at a uniform speed of 30km/h. how fast must the train travel the next 30km so as to average 40km/h for the entire trip

Answer 1

Hallo Matey :D

See the attachment!

Hope it helps you ^_^

Answer 2

here total distance , S = 60 km

let first distance be , S1 = 30 km
and first speed of the train be, V1 = 30 km/hr

now let the second distance be , S2 = 30km
and spedd in the second case be V2 = ?

let t1 and t2 be the time reqd in both cases respectively

therefore total time taken , t = t1 + t2


=S1/V1 + S2/ V2

HENCE AVERAGE SPEED

=total distance covered / total time taken

= S1 +S2 / ( t1 + t2 )

= S1 + S2 / ( S1/V1 + S2/V2)

= 30 + 30 / ( 30/30 + 30/V2)

= 60 / [( V2 + 30) / V2]

= (60 × V2) / (V2 + 30)

but it is given thar avg speed = 40 km/hr

hence we have

40 = (60 × V2) / (V2 + 30)

40V2 + 1200 = 60V2

1200 = 20V2

V2 = 1200/20 = 60 km/hr


hence the speed in second case will be 60 km/hr