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Two point masses of 36 g and 72 g lie on the x-axis at the positions (2 cm, 0) and (5 cm, 0) respectively. Find the coordinates of their centre of mass.

1. (4, 0)
2. (4.5, 0)
3. (3.5, 0)
4. (3, 0)

Correct answer: (4, 0)

Solution

x_cm = (36*2 + 72*5)/(36 + 72) = (72 + 360)/108 = 432/108 = 4 cm, so the centre of mass is at (4, 0).

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