# Physics formula question

• Mar 29th 2007, 12:15 PM
star4822
Physics formula question
Somebody please help me out with this. Nobody I know can help me.

An airplane cruises at 120 km/h in still air. One day, when the wind was blowing steady from the west, the airplane travelled west(flying INTO the wind) and landed at its destination after 1.5 h. The airplane's return trip(flying WITH the wind) was only 1.0 h long. On both legs, the airplane travelled at its cruising speed(measured with respect to the air surrounding the plane)

A) Write a system of equations that would allow you to determine the speed of the wind blowing that day and the distance travelled each way.

B) Indicate what the variable X and Y represent.

Any help would be very appreciated!!
• Mar 30th 2007, 05:11 AM
earboth
Quote:

Originally Posted by star4822
...

An airplane cruises at 120 km/h in still air. One day, when the wind was blowing steady from the west, the airplane travelled west(flying INTO the wind) and landed at its destination after 1.5 h. The airplane's return trip(flying WITH the wind) was only 1.0 h long. On both legs, the airplane travelled at its cruising speed(measured with respect to the air surrounding the plane)

A) Write a system of equations that would allow you to determine the speed of the wind blowing that day and the distance travelled each way.

B) Indicate what the variable X and Y represent....

Hello,

let x be the speed of the wind in km/h
let y be the distance in km

If d is the distance, t the time and v the speed then you should know that the speed is defined by:
Code:

``` d --- = v  that means  t       d  t = ---       v```
Plug in the values you know into this last equation and you'll get 2 different equations:
Code:

```        y 1.5 = --------       120 - x         y 1.0 = --------       120 + x```
180 - 1.5x = y
120 + x = y

You'll get x = 24 km/h and y = 144 km

EB