Calculating Magnetic Force on a Charged Particle

[roam]

Homework Statement

A particle of mass M=2x10^-25 kg, charge Q=8e, and velocity vector v=1.0x10⁵ m/s j enters a uniform magnetic field of strength B=2.5 T. The magnetic firld vector B lies in the x-y plane at an angle of [tex]\alpha =70[/tex] degrees to the x-axis.

What is the magnitude of this initial force exerted on the particle.

Homework Equations

[tex]F=|q|vB sin \theta[/tex]

The Attempt at a Solution

I used the above formula and got:

8(1.6 x 10^-19) x 10⁵ x 2.5 sin 70 =3 x 10^-13

But the correct answer must be 1.1 x 10^-13. What's the problem? I used the correct equation for magnitude of the magnetic force on a charged particle moving in a magnetic field, so why am I getting the wrong answer?

 

[Quinzio]

The angle must between what and what ?

Draw on piece of paper, the force lines and the v vector.

You can't expect the numbers to be always ready to be plugged in :(
Referred in general, not only you.