Homework Help: physics

Posted by Lindsay on Saturday, December 24, 2011 at 7:18pm.

In order to change the angular momentum of an object, it is necessary to apply
a. a net force to the object.
b. a net torque to the object.
c. a centripetal acceleration to the object.
d. both a net force and a net torque to the object.

We have three vectors, labeled A, B, and C. A points due west, B points due north, and C points due east. We don’t know their relative magnitudes. We find the cross product of each of these vectors with a vector which points due south (D). Rank the three cross products ( ) from smallest to largest in terms of their vertical component, taking the sign of the component into account.
g. You cannot tell with the given information

physics - Damon, Saturday, December 24, 2011 at 7:19pm
To change angular momentum requires a moment(torque)
physics - Damon, Saturday, December 24, 2011 at 7:32pm
LOL, yes you can tell
first B X D
the angle between B and D is 180, and the sine of 180 is zero
therefore B X D = 0
that was easy

Now A X D
rotation from A to D is + 90 degrees, so A X D is UP, positive

But C X D
rotation from C to D is negative 90 degrees, cross product down
C X D is DOWN, negative
Thus
in order
CXD negative
BXD zero
AXD positive

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