Answer
1.66m/s, 25$^o$ relative to the river.
Work Step by Step
Let the flow of the river be in the x direction and "across the river" be in the y direction.
Let H denote Huck, R the raft, and B the Bank. The pair “HB”, for example, represents Huck’s motion relative to the Bank.
$$ \vec{v_{HB}} = \vec{v_{HR}} + \vec{v_{RB}} $$
$$= (0, 0.70 m/s) + (1.50 m/s, 0) = (1.50 m/s, 0.70 m/s)$$
$$ \vec{v_{HB}} = (1.50 m/s, 0.70 m/s)$$
Find the magnitude using the Pythagorean Theorem and the direction using the definition of the tangent.
$$ v_{HB} = 1.66 m/s. $$
The angle is at 25$^o$ relative to the river.
