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Two persons Pand crosses the river starting from point A on one side to exactly opposite point B on the other bank of the river. The person P crosses the river in the shortest path. The persone crosses the river in shortest time and walks back to point B. Velocity of river is 3 kmph and speed of each boat is 5 kmph w.r.t river. If the two persons reach the point B in the same time, then the speed of walk of Q is |
Answer» Solution : `t_(p)=(d)/(sqrt(V_(B)^(2)-V_(w)^(2)))=(d)/( sqrt(5^(2)-3^(2)))=(d)/(4)` `t_(Q)=(d)/(V_(B))=(d)/(5), t_(Q)+Deltat` `(d)/(4)=(d)/(5)+(X)/(V_("MAN")) "" "But" x=V_(w)(d)/(V_(B))` `(d)/(4)=(d)/(5)+(V_(w)d)/(V_(B)V_("man")) "" (d)/(4)=(d)/(5)+(34)/((5)V_("man"))` `(1)/(4)-(1)/(5)=(3)/(5_("man")) ""...(1)/(20)=(3)/(5V_("man"))` `V_("man")=((3)(20))/(5)=12` kmph |
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