Motion in a Plane - Result Question 53
56. A boat which has a speed of $5 km / hr$ in still water crosses a river of width $1 km$ along the shortest possible path in 15 minutes. The velocity of the river water in $km / hr$ is
[2000, 1998]
(a) 3
(b) 4
(c) $\sqrt{21}$
(d) 1
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Answer:
Correct Answer: 56. (a)
Solution:
- (a)
Speed along the shortest path
$=\frac{1}{15 / 60}=4 km / hr$
Speed of river $v=\sqrt{5^{2}-4^{2}}=3 km / hr$
