A particle undergoes two displacements. The first has a

magnitude of 150 cm and makes an angle of 120° with

the positive x axis. The resultant displacement has a magnitude

of 140 cm and is directed at an angle of 35.0° to

the positive x axis. Find the magnitude and direction of

the second displacement.

Verified Answer :

First you need to draw the picture of the problem to better understand it. Like the one bellow. 

In this task you have 2 sides of triangle and we can calculate angle between them. Angle between them is 120 - 35 = 85 degrees.

Once you have those 3 variables you can calculate third side of triangle using cosine law.
a - second displacement
b - first displacement
c- resultant displacement.

\(a^{2} = b^{2}+ c^{2}-2*b*c*cos85\)
now we just need to calculate this.
\(a^{2} = 38439.458\)
a = 196

now, we use cosine law again to find the angle between second and first displacement.
\(\alpha = 45.36\) degrees

The angle marked with "?" in the graph is our direction angle. We will call it \(\beta\)

\(\beta =90-30-45.36 = 14.64\)

Second displacement has magnitude of 196 and a direction of -14.64 with positive x axis