Determine the speed of block G, if the block Z is moving up with a velocity of 20 ft/s. The mass of the cord can be assumed negligible.

1) 15 ft/s
2) 20 ft/s
3) 30 ft/s
4) 40 ft/s

There is one cord in this system having segments which are changing length. Position coordinates S_G and S_Z will be used since each is measured from a fixed point (C or D) and extends along each block's path of motion. S_Z is directed to point E since motion of Z and E is the same.

So the total length of the cord at any time is L = S_G+ 3S_Z, neglecting the arc distance on the pulley because it remains constant.
Taking time derivative yields V_G + V_Z = 0
V_G = -V_Z and V_G = -20 ft/s = 20 ft/s (down).

So, the velocity of block G, V_G = 20 ft/s (down).