Answer:
402 km/h at 51°
Step-by-step explanation:
You want the actual velocity of a plane traveling 400 km/h on a bearing of 45° in a wind of 40 km/h on a bearing of 135°.
The plane's actual velocity is the vector sum of the plane's vector and the wind's vector. It will be the third side of the triangle with the given speeds as two of the sides.
The angle between the wind direction and the plane's direction is 135° -45° = 90°. That means the plane's speed will be the hypotenuse of the right triangle, and can be found using the Pythagorean theorem.
s² = 400² +40² = 161600
s = √161600 ≈ 401.995 . . . . . km/h
The wind adds an angle to the plane's bearing that can be found using the sine relation:
Sin = Opposite/Adjacent
sin(θ) = 40/400 = 0.1
θ = arcsin(0.1) ≈ 5.7°
Adding this angle to the heading of the airplane gives its ground-track heading as ...
45° +5.7° = 50.7° ≈ 51°
The actual velocity of the plane is about 402 km/h on a heading of 51°.