Kinematics Question 331
Question: A boat crosses a river with a velocity of 8 km/h. If the resulting velocity of boat it’s 10 km/h then the velocity of river water is [CPMT 2001]
Options:
A) 12.8 $kmh^{-1}$
B) 6 $kmh^{-1}$
C) 8 $kmh^{-1}$
D) 10 $kmh^{-1}$
Show Answer
Answer:
Correct Answer: B
Solution:
The boat is sent across river with velocity 8km/h with respect to river perpendicular to it.
Hence $\overrightarrow {v _{br}}=8 \hat{j}$
Let the velocity of river $\overrightarrow{v _{r}}= v\hat{i}$
Hence the resultant velocity of boat = $\overrightarrow{v _{br}} + \overrightarrow{v _{r}} = \sqrt{\overrightarrow{v^2 _{br}} +\overrightarrow{v^2 _{r}}}$
⟹10=$\sqrt{8^2+v^2}$
⟹v=6km/h
BETA
