Originally Posted by **gwendalagan** hi!
I really need help in solving this problem. i do not know hot to get the y and z components of the magnetic field vector. who can help me please?
A 2.5 nC particle of mass 5.25x10^-6 kg moves through a uniform magnetic field of 7.5 T directed down at 30 degrees in the y-z plane. find the force on the particle at the instant its velocity is 8.0x10^4 m/s along the y axis. |

B is directed downward (aka in the negative z direction) at an angle of 30 degrees below the +y, so $\displaystyle B_y = B ~ cos(30)$ and $\displaystyle B_z = - B ~ sin(30)$.

If it helps you to visualize it recast this into the form that the field is 30 degrees below the +x axis. Then $\displaystyle B_x = B ~ cos(30)$ and $\displaystyle B_y = - B ~ cos(30)$.

-Dan