Physics Two Dimensional Motion Question 201
Question: A boat B is moving upstream with velocity 3 m/s with respect to ground. An observer standing on boat observes that a swimmer S is crossing the river perpendicular to the direction of motion of boat. If river flow velocity is 4 m/s and swimmer crosses the river of width 100 m in 50 sec, then
Options:
A) velocity of swimmer w.r.t ground is $ \surd 13,,m\text{/}s $ B) drift of swimmer along river is zero C) drift of swimmer along river will be 50 m D) velocity of swimmer w.r.t ground is 2 m/s
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Answer:
Correct Answer: A
Solution:
[a] $ \vec{v} _{SB}=v,\hat{j}=\vec{v} _{s}+3,\hat{i} $
$ {\vec{v} _{S}}=v\hat{j}-3,\hat{i}\text{ and }v=\frac{100}{50}=2m/s $
$ \
Therefore !!|!!{{\vec{v}} _{s}}!!|!!\text{ =}\sqrt{{v^{2}}+{{( 3 )}^{2}}}=\sqrt{v^{2}+9}=\sqrt{13}\text{ m/s} $
$ \text{Drift = 50}\times \text{3=150 m} $
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