Answer:
D
Step-by-step explanation:
As is often the case with multiple choice questions, a simple check of the reasonableness of the answers will identify the correct one.
Here, the key is that the center of mass will be at the non-zero mass if one of them is zero. Assuming m2 = 0, the center of mass will have coordinates (x1, y1).
Checking the offered expressions when m2=0, we have ...
A. (m1x1/(2m1), m1y1/(2m1)) = (x1/2, y1/2) ≠ (x1, y1)
B. (m1(x1 +x2)/(2m1), 0) = ((x1+x2)/2, 0) ≠ (x1, y1)
C. (m1x2/m1, m1y2/m1) = (x2, y2) ≠ (x1, y1)
D. (m1x1/m1, m1y1/m1) = (x1, y1) . . . . . the answer we're looking for