Question on Finding Resultant and Direction of a Moving Article

Topic : Trigonometry

Question : Airplane is moving with speed 400knot due East and wind 50knot due North East . Find the resultant and direction .

Solution :

400 ->E
50 ->NE
Angle between East and North direction is 45º
Hence angle between 400 and 50 is 45º



We have a formula for the resultant of two forces (velocities) P and Q

R² = P² + Q² +2PQCosθ, θ being the angle between P and Q

P = 400; Q = 50; θ = 45

R² = 400² + 50² + 2(400)(50)Cos45
= 160000 + 2500 + 40000 * 0.7071
= 190784

So resultant R = √(190784) = 436.788 = 436.8

To find the direction :

The angle Φ is in between R and P

Q Sin θ
So tan Φ = --------------------
P + Q Cos θ

50 Sin 45
tan Φ = ------------------------- = 0.0812 => Φ = tanˉ ¹ 0.0812 => 4.65
400 + 50 Cos 45

Here Φ is the angle between R and P
and Φ = 4.65 , if resultant motion is away due East.

That is same as
90 – 4.65 due North
So 85.35 ≈ 85.4 due North

Hence Solution is 436.8 due 85.4º North

Hope the Answer and Explanation will be helpful for you.