Question

A boat travels at the rate 25 in still water. If the rate of the current is 18 , what is the rate of the boat
a. upstream
b. downstream
c. across the river?

Answer 1

Answer on question #75693, Physics / Molecular Physics | Thermodynamics

A boat travels at the rate 25 in still water. If the rate of the current is 18, what is the rate of the boat

a. upstream

b. downstream

c. across the river?

Solution

a. Rate of the boat upstream: $v = v_{\text{boat}} - v_{\text{current}} = 25 - 18 = 7$ .

b. Rate of the boat downstream: $v = v_{\text{boat}} + v_{\text{current}} = 25 + 18 = 43$ .

c. Rate of the boat across the river:

By the Pythagorean theorem $v^2 = v_{\text{boat}}^2 + v_{\text{current}}^2$

$$v = \sqrt {v ^ {2} _ {\text {b o a t}} + v ^ {2} _ {\text {c u r r e n t}}}$$ $$v = \sqrt {2 5 ^ {2} + 1 8 ^ {2}} \cong 3 0. 8$$

Answer: a. 7

b. 43

c. 30.8