Question

You are piloting a small airplane in which you want to reach a destination that is 750 km due north of your starting location. Once you are airborne, you find that (due to a strong but steady wind) to maintain a northerly course you must point the nose of the plane at an angle of 22 west of true north. From previous flights on this route in the absence of wind, you know that it takes you 3.14 h to make the journey. With the wind blowing, you find that it takes 4.32 h. A fellow pilot calls to ask you about the wind velocity (magnitude and direction). What is your report? FYI so you can check yourself the answers are 101 km/h at 62 degrees east of south.

Answer 1

Answer:

v_wind = 101.46 km / h   ,  θ = 61.8

Explanation:

This is a velocity composition exercise.

Let's do the problem in parts. Let's start by knowing the speed of the plane without air.

           v = d / t

           v = 750 / 3.14

           v = 238.85 km / h

This is the speed of the plane relative to the Earth and it does not change.

In the second part, when there is wind, the travel time is greater than when there is no wind, therefore the wind delays the plane. To be more general, suppose that the wind has two components vₓ and $v_{y}$

Let's use trigonometry to find the components of the plane's speed

          cos θ = v_N / v

          sin θ  = v_W / v

          v_N = v cos θ

          v_W = v sin θ

           

let's calculate

          V _N = 238.85 cos 22 = 221.46 km / h

           v_W = -238.85 sin 22 = -89.47

the negative sign is because the plane is going west and the positive sign is the east direction.

As it indicates that the destination of the avine is towards the north, the x component of the wind must be

              vₓ - v_W = 0

              vₓ = v-w

              vₓ = 89.47 km / h

in the direction to the East.

Now let's analyze the component of the wind in the Nort-South direction,

Indicate the travel time, let's calculate the speed that the component must have the speed of the plane

             v_total = d / t

             v_total = 750 / 4.32

             v_total = 173.61 km / h

This is the final speed of the plane, which can be written

              v_total = v_n - vy

               vy = v_n - v_total

               vy = 221.46 - 173.61

               vy = 47.85 km

this component is directed towards the south

Let's use the Pythagorean Theorem, to find the magnitude

             v_wind² = vₓ² + vy²

             v_wind = √ (89.47² + 47.85²)

             v_wind = 101.46 km / h

the address will then be found using trigonometry

             θ = Vy / vx

             θ = tan⁻¹ (vy / vx)

             θ = tan⁻¹1 (47.85 / 89.47)

             θ = 28.14

Therefore, the magnitude of the wind speed is 101.5 km / h and its direction is 28º south of the East, to give this value

                  90- θtea = 90- 28.2

                  θ = 61.8

East of South