Two cyclists are travelling at constant speeds around a 400 m track in opposite direction. The speed of Jeff is 1.5 times the speed of Rob. The cyclists find they meet every 20 s. What is the speed of Jeff?

Question

A) 9.0 m/s
B) 12 m/s
C) 13 m/s
D) 20 m/s
E) 30 m/s

Answer 1

relative speed: 2.5xRobbspeed
they meet each cycle 20 sec

v=400/20=20m/s=relative speed.
but relative speed=Vrob+1.5Vrob
20m/s=2.5 Vrob
Vrob= 8m/s
VJeff=12m/s