Q. A goa can travel at a speed of 8 $kmh^{- 1}$ in still water on a lake. In the flowing water of a stream, it can move at $8kmh^{- 1}$ relative to the water in the stream. If the stream speed is 3$kmh^{- 1}$, how fast can the boat move past a tree on the shore in travelling (i) upstream (ii) downstream?
A) $5kmh^{- 1}$ and $11\ kmh^{- 1}$
B) $11kmh^{- 1}$ and $5\ kmh^{- 1}$
C) $8kmh^{- 1}$ and $8\ kmh^{- 1}$
D) $5kmh^{- 1}$ and $5\ kmh^{- 1}$.
Explanation
(a) For upstream motion, km$h^{- 1}$=5$kmh^{- 1}$
For downstream motion,
$v = (8 + 3)kmh^{- 1} = 11kmh^{- 1}$
Reviewed by Dr. Abubacker
Physics Educator & NEET/JEE Specialist
Ph.D. in Physics with 19+ years of teaching experience.