Question

53. On a 60 km stretch of road a cyclist travels first 20
km at a uniform speed of 20 km h-1. How fast must
he travel the remaining distance so that his average
speed is 10 km h-1 for the entire trip.​

Answer 1

Answer:

Given:

Total distance =60km

Average speed of entire journey=20km/h

Total Time taken =

total distance/average speed

=60/10

=6hr

Case :1

Let us CALCULATE time taken to cover first 20km

Speed=20km/h

Distance=20km

T=distance/ speed=20/20

=1hr -----equation ( 1)

Case: 2

Let us CALCULATE time taken to travel next 40 km

Let speed be =Xkm/ h

X=40 KM/t

t=40/X hours ----equation( 2)

Total time = add equation 1 and 2

=1 +40/X

Since total time =3 h

6 =1 +40/X

6-1 =40/X

5 =40/X

X=8 km/h

Therefore cyclist should travel next 40 km distance at a speed of 8 km/h.

Hope it is clear