What is the scalar product V_1(DOT)V_2 ?

[Rellsun]

Homework Statement

Vector V_1 points along the z axis and has magnitude V_1 = 80. Vector V_2 lies in the xz plane, has magnitude V_2 = 51, and makes a -49^o angle with the x-axis (points below x axis)

Homework Equations

A.B=ABCos(theta)=A_xB_x+A_yB_y+A_zB_z

Cos(theta)=(A_xB_x+A_yB_y+A_zB_z)/AB

The Attempt at a Solution

im not really sure where to go from here I am not sure if those equations are useful

 

[kuruman]

The equations are indeed useful. Find the x,y and z components of each vector, then apply the first equation that you posted.

 

[Rellsun]

ok that helps a lot i don't know why i did do that. but how do you find the z component of the V_2=51?

 

[kuruman]

Vector V_2 lies in the xz plane, has magnitude V_2 = 51, and makes a -49^o angle with the x-axis (points below x axis)

Draw yourself two axes in the plane of the paper. Label the horizontal one x and the vertical one z (instead of the usual y). Draw the vector as indicated. Can you find its x and z components?

 

[Rellsun]

ahh thanks that makes much more sense. i got the final answer to be -3079.2 which is indeed correct. the help is appreciated.