Cross Product of Antiparallel Vectors: qvXb Maybe Not?

[SoulofLoneWlf]

qvxb maybe not??

Homework Statement

consider the example of a positive charge moving in the -z direction with speed with the local magnetic field of magnitude in the +z direction. Find , the magnitude of the magnetic force acting on the particle.
Express your answer in terms of , , , and other quantities given in the problem statement.

Homework Equations

f=qvXb yet this does not work ;/
This would be true if and were orthogonal. Instead, they are antiparallel--look back at the definition of the cross product if you still have trouble.

The Attempt at a Solution

 

[Doc Al]

f=qvXb yet this does not work ;/
This would be true if and were orthogonal.

$$\vec{F} = q\vec{v}\times \vec{B}$$

works just fine, but that only equals qvB when v and B are orthogonal.

Instead, they are antiparallel--look back at the definition of the cross product if you still have trouble.

Sounds like good advice to me.

 

[SoulofLoneWlf]

$$\vec{F} = q\vec{v}\times \vec{B}$$

works just fine, but that only equals qvB when v and B are orthogonal.

Sounds like good advice to me.

thank these things just confuse me at time :) lol easy to study for hard to do some how :/