A 1.0kg cart moves east at 2.0ms−1 while a 3.0kg cart moves east at 1.0ms−1. A third cart of mass 2.0kg is to be added so that the combined center-of-mass velocity of all three carts is 1.0ms−1 east. What velocity must the third cart have just before it joins the system?
a) 1.5ms−1 east
b) 0.50ms−1 west
c) 0.50ms−1 east
d) 1.0ms−1 east