If a river current is 8.0 m/s, and a boat is traveling 10.0 m/s upstream, what is the boat’s speed relative to the riverbank?

The relative speed of the boat is found to be - 2 m/s or 2 m/s in opposite direction to the river current.

Explanation:

Let us, consider the direction of river as the reference of positive direction. Hence,

Speed of River = Vr = 8 m/s

Since, the boat is traveling upstream. The upstream direction means that the boat is traveling in the opposite direction of the river current. Therefore, its direction will be negative. Hence,

Speed of boat = Vb = - 10 m/s

Now, the relative speed will be the vector sum of both speeds, with relative directions:

Relative Speed = V = Vr + Vb

V = 8 m/s - 10 m/s

V = - 2 m/s

This shows that the magnitude of speed of boat is 2 m/s and its direction will be opposite to that of river current.

54 degrees incident angle = reflected angle

angle is from normal turned to line of ray