# Thread: Past Year Exam Question

1. ## Past Year Exam Question

Hi guys,

Anyone know how to solve this?

Two particles A and B, of masses m and 4m respectively, lie on a smooth horizontal surface. Their position vectors with respect to the origin in Cartesian coordinates, are -3i and i , respectively.
a) Find the position vector of their centre of mass.

Thanks,
WeiJing

2. ## Re: Past Year Exam Question

$\displaystyle \bar{x} = \frac{\sum m_i x_i}{\sum m_i}$