Calculating Velocity of Center of Mass for Two Particles

[mikefitz]

If a particle of mass 5.3 kg is moving east at 10 m/s and a particle of mass 19 kg is moving west at 10 m/s, what is the velocity of the center of mass of the pair?

This one should be simple, here is my work:

Vcm = (m1v1 + m2v2) / (m1 + m2)

(-5.3kg*10m/s + 19kg * 10m/s) / -5.3 + 19

= 10m/s

This is wrong according to my book, why isn't this velocity of the center of mass correct ? Thanks again for all the help tonight everyone.

 

[OlderDan]

A sign problem perhaps?

 

[mikefitz]

I thought since the 5.3kg particle was moving east it would have a different sign (-). In any case, the answer is still the same with a positive sign...

 

[OlderDan]

I thought since the 5.3kg particle was moving east it would have a different sign (-). In any case, the answer is still the same with a positive sign...

The velocity direction gives you a (-) for the velocity. The mass is always positive.