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## Homework Statement

Four particles of mass 1 Kg each, are moving on a plane with the velocities given in the figure.

## Homework Equations

## The Attempt at a Solution

First I calculated the position of the CoM:

X

_{cm}=7/4(i + j)

Then I calculated the velocity of the CoM:

V

_{cm}= ½i + ¼j

For the internal energy I did the following:

K

_{int}= (1/2)(1.5

^{2}) + (1/2)(1.3

^{2}) + (1/2)(1.3

^{2}) + (1/2)(1.2

^{2}) = 23,5J

But the answer is 22,9 J. And for the internal angular momentum I do not actually know with respect to which point I should calculate it. Any hint would be appreciated. Thank you.

#### Attachments

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