# Momentum combination

 P: 142 1.)Let us assume that the blocks are in motion, and the x-components of their momenta at a certain moment are $$p_1$$ and $$p_2$$, respectively. (there's a pic attached) Find the x-component of the velocity of the center of mass at that moment. Express your answer in terms of $$m_1,m_2,p_1, p_2$$ my answer is $$v_{cm} = \frac{m_1*p_1+m_2*p_2}{m_1+m_2}$$ but it's incorrect and i dont understand why. i think p stands for point particle. also, i have one more quick quesiton: 2.)Suppose that $$v_{cm} = 0$$. Therefore, the following must be true A.) $$p_1 = p_2$$ B.) $$v_1 = v_2$$ c.) m1 = m2 d.) none of the above for this one, i think that if it's equal to zero, both masses should be equal, is this correct? Attached Thumbnails