Magnitude of force on charged particle

[Cici2017]

Homework Statement

Homework Equations

The Attempt at a Solution

I know the equation of force on a moving charge in a magnetic field is F=BqV...
Why is the answer A ?

 

[cnh1995]

I know the equation of force on a moving charge in a magnetic field is F=BqV...

What is the original vector equation for this force?

 

[Cici2017]

What is the original vector equation for this force?

F=qvBsinθ ?

 

[cnh1995]

F=qvBsinθ ?

Yes. It's actually q(vxB), where vxB is the cross product of v and B.
What is the cross product of v and B in this problem?

 

[Cici2017]

Yes. It's actually q(vxB), where vxB is the cross product of v and B.
What is the cross product of v and B in this problem?

0?

 

[cnh1995]

0?

Yes.

 

[Cici2017]

Yes.

Thank you!