The expression for the speed v of the the river relative to the shore is v = (v₁ + v₂)/2 and its value v = 4.76 m/s
Since v = speed of water relative to the shore, s = speed of boats relative to the river, v₁ = speed of first boat relative to the shore = 3.85 m/s and v₂ = speed of second boat relative to the shore = 5.66 m/s.
Since both boats are moving in opposite direction s relative to the river, their speeds relative to the shore are
v₁ = v + s (1) and v₂ = v - s (2)
To find the speed of the river relative to the shore v, we add (1) and (2),
So, v₁ = v + s (1)
+ v₂ = v - s (2)
v₁ + v₂ = 2v
v = (v₁ + v₂)/2
Substituting the values of the variables into the equation, we have
v = (3.85 m/s + 5.66 m/s)/2
v = 9.51 m/s/2
v = 4.755 m/s
v ≅ 4.76 m/s
So, the expression for the speed v of the the river relative to the shore is v = (v₁ + v₂)/2 and its value v = 4.76 m/s
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