Angular Momentum multiplication

[cowmoo32]

At a particular instant the location of an object relative to location A is given by the vector A = < 7, 6, 0 > m. At this instant the momentum of the object is p = < 20, 8, 0 > kg · m/s. What is the angular momentum of the object about location A?

According to my book, angular momentum is found by multiplying r*p with r perpindicular from the location to the line of motion. how do I find r perpindicular?

 

[OlderDan]

At a particular instant the location of an object relative to location A is given by the vector A = < 7, 6, 0 > m. At this instant the momentum of the object is p = < 20, 8, 0 > kg · m/s. What is the angular momentum of the object about location A?

According to my book, angular momentum is found by multiplying r*p with r perpindicular from the location to the line of motion. how do I find r perpindicular?

Does your book say anything about the cross product of two vectors and the definition of angular momentum in terms of a cross product?