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three forces of 150, 200 and 250 pounds respectively are in equilibrium. what are the angles between them?

 May 14, 2016

Best Answer 

 #1
avatar+36916 
+5

Egads !  I do not know that I could figure this one out without a little more info......but I will try....lets put the 250 pound force on the x-axis

 

Forces vertical =  200 sin x      &   150 sin y      Since the  250 pound will not exert any vertical force because it is strictly horizontal these two must be equal and opposite THEN   200 sin x = - 150 sin y    ... .(EQUATION 1)

 

Horizontal forces   200 cos x   &  150 cos y    and 250    I wil have to assume that the two smaller horizontal forces are balancing the larger 250 force

 so   200 cos x + 150 cos y = 250    ... . (EQUATION 2)

 

We now have two equations with two unknowns and should be able to solve for the angles x and y.....

 

I'm missing some trig rule to figure out these two equations, BUT by successive trial and elimination (i.e interprolation)  I come up with (approximately)  

250 horizontal to the right

200 @ 143.77 degrees

150 @  232     degrees     Sorry.....I got STUCK !

 May 14, 2016
 #1
avatar+36916 
+5
Best Answer

Egads !  I do not know that I could figure this one out without a little more info......but I will try....lets put the 250 pound force on the x-axis

 

Forces vertical =  200 sin x      &   150 sin y      Since the  250 pound will not exert any vertical force because it is strictly horizontal these two must be equal and opposite THEN   200 sin x = - 150 sin y    ... .(EQUATION 1)

 

Horizontal forces   200 cos x   &  150 cos y    and 250    I wil have to assume that the two smaller horizontal forces are balancing the larger 250 force

 so   200 cos x + 150 cos y = 250    ... . (EQUATION 2)

 

We now have two equations with two unknowns and should be able to solve for the angles x and y.....

 

I'm missing some trig rule to figure out these two equations, BUT by successive trial and elimination (i.e interprolation)  I come up with (approximately)  

250 horizontal to the right

200 @ 143.77 degrees

150 @  232     degrees     Sorry.....I got STUCK !

ElectricPavlov May 14, 2016
 #2
avatar+33616 
0

The analysis below should help you to work out the angles between them:

 

angles1

angles2

.

 May 15, 2016
 #3
avatar+36916 
0

Though I got the same answer via trial and error, I wanted to do it mathematically like you did...but you lost me between the step 4 lines from the bottom and the step 3 lines form the bottom.....how did you 'simplify' that?

Thanx !

ElectricPavlov  May 15, 2016
 #4
avatar+33616 
0

I just used a piece of software to do it for me!  However, here is the derivation:

 

derivation

.

 May 15, 2016
 #5
avatar+36916 
0

Ahhhhhhh!   I got to that point and it seemed like it was gonna be big a drawn out ordeal squaring both of those factors...THAT is when I 'trial and error'ed'  it !       Thanx again !

ElectricPavlov  May 15, 2016

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