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Grade 11General Physics

A man crosses a river in a boat in minimum time of 10mins with a drift 120m. If he crosses in shortest path he takes 12.5mins. Find (i) width of river (ii) velocity of boat w.r.t water (iii) speed of current.

Profile image of Pranali Vira
13 Years agoGrade 11
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3 Answers

Profile image of Monil Shah
13 Years ago

Width of river is 187.5,speed of boat ww.r.t is 0.25 ,velocity of current is 0.2.

 

All speed are in m/ s and distance in m

Profile image of Arun Kumar
12 Years ago
velocity of river=120m/10min=12m/min
now for the man in second case(shortes path
vx^2+vy^2=v^2 where v is magnitude of man's velocity

vy=12m/min since its the shortest path
so vx=root(v^2-12^2)

for the shortest time
d=10*v

10v=12.5*root(v^2-12^2)

v=root(12.5^2*10^2/(12.5^2-10^2))
v=12*12.5/(2.5*22.5)

d=10*v

Profile image of KAPIL MANDAL
11 Years ago
Thank you sir for this answer. Thank you very much.