# Re: Physics

posted by on .

Posted by COFFEE on Friday, March 30, 2007 at 4:25am.

A 1.1 kg particle-like object moves in a plane with velocity components Vx = 30 m/s and Vy = 90 m/s as it passes through the point with (x, y) coordinates of (3.0, -4.0) m.

(a) What is its angular momentum relative to the origin at this moment?
_____ kg*m^2/s k
(b) What is its angular momentum relative to the point (-2.0, -2.0) m at this same moment?
_____ kg*m^2/s k

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i drew a points on a flat xy plane.. but im not sure if i drew it correctly. i have the Vx component towards the positive X direction and the Vy towards the negative Y direction.

angular momentum = r x p
r x p = m (r x v)
......= 1.1 (r x 30)
......= 1.1r x 30
-33 = 1.1r
-30 = r

.. im stuck.. help!

* Physics - bobpursley, Friday, March 30, 2007 at 7:52am

1. Angular momentum= R x mV Where mV is the linear momentum, x is the cross product, and R is the position vector.
= m270k + m 120k
= m*390 k
check my thinking.

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thank you, i understand that part.
..but if the origin was changed, in this case in part b: (-2.0, -2.0) m

how would the 'Angular momentum= R x mV' equation change? is the linear momentum the one affected?

R changes: New R is R-Ro where Ro is the new point for the origin.

You now have M=(R-Ro)xV

thanks! got it :)

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