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CBSE Class 11-science Answered

a boat's speed in still water is 20km/h .if the boat is to travel directly across a river whose current has a speed of 12km/h ,at what upstream angle must the boat head?
Asked by pawankumardas15492 | 22 Jul, 2022, 22:24: PM
answered-by-expert Expert Answer
Figure shows the vector diagram for boat velocity and river velocity .
 
Let the boat travels in a direction that makes angle θ with the bak of river as shown in figure.
 
If the boat is to travel across the river perpendicular to the flow direction,
 
then the resolved component (20 cosθ ) km/h of boat velocity along the river bank
 
should be equal to river velocity vector as shown in figure.
 
20 cosθ = 12   or   cosθ = 0.6    
 
Hence θ = cos-1 (0.6 ) = 53o
Answered by Thiyagarajan K | 23 Jul, 2022, 07:35: AM

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