Question

Danny sails a boat downstream. The wind pushes the boat along at 21 km/hr. The current runs downstream at 15 km/hr. What is the actual velocity of the boat?

A) 6.0 km/hr, downstream
B) 1.4 km/hr, downstream
C) 310 km/hr, downstream
D) 36 km/hr, downstream

Answer 1

D. 36 km/hr, downstream

you add the boats speed of 21kph to the rivers speed of 15kph to get your answer

Answer 2

Answer: D) 36.0 km/hr, downstream

Explanation:

For downstream motion of the boat, the actual velocity of the boat is the sum of velocity of the water current and the velocity of the boat due to pushed by wind.

Velocity of water current, v = 15 km/h

Velocity of the boat going downstream, u = 21 km/h

Actual velocity of the boat = v'

v' = v + u

⇒v' = 15 km/h + 21 km/h

⇒u = 21 km/h +15 km/h = 36.0 km/h downstream

Thus, the correct answer is option D.