# Homework Help: What are the x and y components of the velocity of the CM of the two bodies?

1. Nov 16, 2009

### jayced

1. The problem statement, all variables and given/known data

Body A of mass 3 kg is moving int he x+ direction with a speed of 14 m/s. Body B of mass 4 kg is moving in the -y direction with a speed of 7 m/s. What are the x and y-components of the velocity of the CM of the two bodies?

2. Relevant equations

CMx=m1x1x+m2x2/m1+m2

3. The attempt at a solution
I am not getting the answer when I enter the figures into the equation. Is this the right equation? Please help it seems simple once I get the right equation.

2. Nov 17, 2009

### PhanthomJay

It seems from the solution that the 3Kg and 4kg blocks are reversed. Body A appears to be 4 kg, and Body B appears to be 3 kg.

3. Nov 17, 2009

### jayced

I'm still confused so if they are reversed can I ask what equation would I use to calculate x and y components?

4. Nov 17, 2009

### ehild

The coordinates of the CM in case of two bodies:

$$x(CM)=\frac{x_1m_1+x_2m_2}{m_1+m_2}$$

$$y(CM)=\frac{y_1m_1+y_2m_2}{m_1+m_2}$$

The same holds for the components of velocity:

$$V_x(CM)=\frac{v_{x1}m_1+v_{x2}m_2}{m_1+m_2}$$

$$V_y(CM)=\frac{v_{y1}m_1+v_{y2}m_2}{m_1+m_2}$$

ehild