 #1
NovatoOfPhysica
 2
 1
 Homework Statement:

The system shown in Fig. 26 is in static equilibrium. Use the principle of
virtual work to find the weights A and B. Neglect the weight of the strings and
the friction in the pulleys.
 Relevant Equations:
 Virtual Work Equations
Hi there, this question has already been discussed in this forum, however I do not know how to proceed further and if my reasoning is correct.
I start by imagining a downard displacement of the 1kg weight. As a consequence of this, block A moves upward and to the right. Also, block B moves upward at the same time. So I get the following formulas:
(1) dW = W1cos30dxcos0 + WBcos45dxcos180 = 0
(2) dW = W1sin30dh1cos0 + WAdhAcos180 + WBdhBcos180 = 0
(The last cos is the angle between the Force and the Displacement)
From the first equation I get the correct answer for WB. However, a couple of questions arise. First of all, isn't this form the same as the equation for the tension of both weights? That is, am I not using the principle of virtual work and instead am I using a conventional static method? Secondly, shouldn't there be only one virtual work equation instead of two or am I overthinking? (The last question comes because I watched a video where he could use dx and dy in only one equation if i recall correctly.)
From the second equation I do not know how to continue as I have three different variables dh1, dhA and dhB. What am I missing? Could you give me any hint so I can continue further?
Thank you in advance
PS I do not know how to format this question any tip and I'll try to edit it.