Question

Danny lowers the sails on his boat. He paddles upstream at 19 km/hr. The current is still running downstream at 15 km/hr. What is the actual velocity of the boat? 34 km/hr, downstream 34 km/hr, upstream 4 km/hr, downstream 4 km/hr, upstream

Answer 1

upstream 4 km/h

Step-by-step explanation:

Let's define "upstream" as positive direction for the velocities. Therefore, we have:

`v_1=+19 km/h` is the velocity of Danny paddling, which is positive because it is upstream

`v_2=-15 km/h` is the velocity of the current, which is negative because it is downstream

Velocity is a vector, so we have to calculate the resultant velocity. However, the two velocities are along the same direction (just with opposite sign), so their resultant is given by their sum:

`v=v_1 +v_2 = +19 km/h +(-15 km/h) = +4 km/h`

and the positive sign means the direction is upward.

Answer 2

since the direction of his paddles is opposite of the the direction of the current, so the actual velocity can be calculated by subtracting the velocity of current to to his velocity when paddling
v = 19 - 15
v = 4 since the answer is positive, then the direction is upstream