# Relative velocities

## Homework Statement

The wind is blowing at 72km/h south relative to the earth, and a plane is traveling 320km/h (28 degrees south of west relative to the wind) directly above a city. give displacement from the city in 2h time

## Homework Equations

Plane is P wind is W earth is E

VPW=VPE+VWE

## The Attempt at a Solution

re arrange to find that
VPE=VPW-VWE
VPE=248km/h

The only thing I dont understand is how to determine the new angle of the plane to the earth...

rl.bhat
Homework Helper
Velocities are vectors. You cannot add or subtract them directly.

Hi slpnsldr. Your formula was incorrect. It should look like this
$$\vec{_{p}V_{E}}=\vec{_{p}V_{w}}+\vec{_{w}V_{E}}$$

Notice when you add these relative velocities, the subscript "w" cancel each other out. And that is the only trick to it.

ok, ive figured out my displacement.. but im still unclear about how to find the planes new angle
somethign to do with the sine law?

ok, ive figured out my displacement.. but im still unclear about how to find the planes new angle
somethign to do with the sine law?

Oh, that might be hard to explain without a diagram. Maybe you need to include a diagram.