Question

A river flows due east at 1.70 m/s. A boat crosses the river from the south shore to the north shore by maintaining a constant velocity of 14.0 m/s due north relative to the water.

(a) What is the velocity of the boat relative to shore?
m/s
° (north of east)

(b) If the river is 340 m wide, how far downstream has the boat moved by the time it reaches the north shore in meters?

Answer 1

a)

v = 14.1028 m/s

∅ = 83.0765° north of east

b)

the required distance is 40.98 m

Explanation:

Given that;

velocity of the river u = 1.70 m/s

velocity of boat v = 14.0 m/s

Now to get the velocity of the boat relative to shore;

( north of east), we say

a² + b² = c²

(1.70)² + (14.0)² = c²

2.89 + 196 = c²

198.89 = c²

c = √198.89

c = 14.1028 m/s

tan∅ = v/u = 14 / 1.7 = 8.23529

∅ = tan⁻¹ ( 8.23529 ) = 83.0765° north of east

Therefore, the velocity of the boat relative to shore is;

v = 14.1028 m/s

∅ = 83.0765° north of east

b)

width of river = 340 m,

ow far downstream has the boat moved by the time it reaches the north shore in meters = ?

we say;

340sin( 90° - 83.0765°)

⇒ 340sin( 6.9235°)

= 40.98 m

Therefore, the required distance is 40.98 m