How to find velocity of center of mass without given masses

[gracy]

But in this lecture

First example of car and truck no mass is given but he has solved for velocity of centre of mass.
How?Is there any other alternative way to solve for velocity of centre of mass.

 

[mfb]

He just defined it to be 4m/s (it is his example, he can do that), where the masses or at least the ratio of the masses have to be determined later.

 

[gracy]

Oh! thanks.

 

[Doc Al]

First example of car and truck no mass is given but he has solved for velocity of centre of mass.
How?Is there any other alternative way to solve for velocity of centre of mass.

Looks to me like he's referring to a calculation done in a previous lecture. He's just reviewing the calculation, not doing it here.

 

[nasu]

He is referring explicitly (around 4:20) to an example discussed previously. So the masses were given, I suppose.