What is the solution for relative velocity of sliders?

[Jonski]

Homework Statement

Homework Equations

[/B]
Va = Va/c + Vc
Va = 0.2 + Vc
Vb = Vd

The Attempt at a Solution

I began by finding the instant centre of rotations of AB and CD. Both of these form a right angle triangle and the length of A -> ICab = 200mm and C -> ICcd = 300mm
Va/0.2 * 0.15 = Vb
Vc/0.3 * 0.125 = Vd
Va/0.2 * 0.15 = Vc/0.3 * 0.125
0.75*(0.2+Vc)=0.417(Vc)
Vc = -0.45
Vd = -0.1875m/s = Vb

The answer is 0.0536m/s, but I am not sure why taking the instant centre does not work. Did I mess anything up. Thanks in advance

 

[gneill]

The Attempt at a Solution

I began by finding the instant centre of rotations of AB and CD. Both of these form a right angle triangle and the length of A -> ICab = 200mm and C -> ICcd = 300mm
Va/0.2 * 0.15 = Vb
Vc/0.3 * 0.125 = Vd
Va/0.2 * 0.15 = Vc/0.3 * 0.125
0.75*(0.2+Vc)=0.417(Vc) $~~~~$←
Vc = -0.45
Vd = -0.1875m/s = Vb

The answer is 0.0536m/s, but I am not sure why taking the instant centre does not work. Did I mess anything up. Thanks in advance

I believe that your problem lies at the line indicated above. It appears to me that you've taken velocity Va to be positive to the right and Vc to be positive to the left. Then your Va + Vc = 0.2 and so Va = 0.2 - Vc.

 

[Jonski]

I believe that your problem lies at the line indicated above. It appears to me that you've taken velocity Va to be positive to the right and Vc to be positive to the left. Then your Va + Vc = 0.2 and so Va = 0.2 - Vc.

Oh, thanks. I understand now