What is the Average Velocity of a Ship and the Velocity of the River Current?

[kerol9904]

Homework Statement

A ship goes from A to B at $$v_1=10 km/h$$ and from B to A at $$v_2=16 km/h$$ Find: (1) the average velocity of the ship, and (2) the velocity of the river current.

Homework Equations

$$v_{avg}=(v_1+v_2)/2$$
$$v_{AC}=v_{AB}+v_{BC}$$

The Attempt at a Solution

$$v_{Boat}-v_{Current}=10km/h$$
$$v_{Boat}+v_{Current}=16km/h$$
$$v_{Boat}=13km/h, v_{Current}=3km/h$$
The actual answer for $$v_{Boat}=12.3km/h$$ Why is that?

 

[Doc Al]

What's the definition of average velocity (really average speed)?

 

[kerol9904]

Change in position/Change in time?

 

[Doc Al]

Change in position/Change in time?

Try total distance / time.

$$v_{avg}=(v_1+v_2)/2$$

This only applies to uniformly accelerated motion, which is not what's going on here.

 

[kerol9904]

Ahh... I didn't realize that the equation is only for uniformly accelerated motion. I've got the answer now. Thanks!