Magnatism-Induction problem

[hazim]

Homework Statement

A positively charged particle moves in a circle of radius R in the plane of the page with velocity v when a magnetic field B is into the page. (a) If the magnetic field is increased, will the speed of the charged particle remain the same increase, or decrease?

Homework Equations

The Attempt at a Solution

I just have a problem which is the direction of the velocity I should take.. this problem is number 13 in this site http://www.wellesley.edu/Physics/phyllisflemingphysics/106_p_induction.html, and it's solution is here http://www.wellesley.edu/Physics/phyllisflemingphysics/106_s_induction.html
I didn't understood how to take the sense of v (clock wise or counterclock wise)...hope someone clarify.thanks.

 

[pam]

If B is into the page, the velocity must be counterclockwise for the force to be toward the center of the circle (by the right hand rule).

 

[hazim]

13.

http://www.imagehosting.com/out.php/i1565193_figurefor13.gif

"For a particle to move in a circle, there must be a force into the center of the circle to produce the centripetal acceleration."
thanks pam, i didn't noticed that at first...it's easy