Elimination on velocities and angles

chemic_23 · Jan 29, 2009

Homework Statement

How do you eliminate this?

V3(cos A) + V4(cos 30) = 5 Equation 1
V3(sin A) = -(V4)(sin 30) Equation 2
V3^2 + V4^2 = 25 Equation 3

I let

x= V3 ; y=V4

and I got

x(cos A) + y ((sqrt)3) = 10
-2x(sin A) = y
x^2 + y^2 = 25

but I'm totally stuck... any help?

chaoseverlasting · Jan 29, 2009

Replace value of V₄ from 2 in 1 and 3,

Square equation 1 to get expression for angle A,

Replace value of angle A in eq 3 to get value of V₃

tiny-tim · Jan 29, 2009

chemic_23 said:

x(cos A) + y ((sqrt)3) = 10
-2x(sin A) = y
x^2 + y^2 = 25

Two methods:

i] put x = 5cosB, y = 5sinB

or ii], in this particular case, it seems easier to use the second equation to eliminate y immediately.