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.

Respuesta :

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.

[tex] a^{2} = b^{2}+ c^{2}-2*b*c*cos85 [/tex]
now we just need to calculate this.
[tex] a^{2} = 38439.458[/tex]
a = 196

now, we use cosine law again to find the angle between second and first displacement.
[tex] \alpha = 45.36 [/tex] degrees

The angle marked with "?" in the graph is our direction angle. We will call it [tex] \beta [/tex]

[tex] \beta =90-30-45.36 = 14.64[/tex]

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