Answer to Question #285693 in Physics for kin

Question

can i just use 60 km/hr as average velocity for boat b

Answer 1

No, because the average velocity is zero (it is total displacement, which is zero, divided by total time).

The average speed is total distance, which is 2d, divided by total time:

$$s_B=\dfrac{d+d}{d/30+d/90}=45\text{ km/h}.$$