What is the magnetic force on a proton that is moving at 2.5 107 m/s up through a magnetic field that is 0.12 t and pointing toward you? the charge on a proton is 1.6 10-19 c. a. 4.0 10-12 n down b. 4.0 10-12 n up c. 4.8 10-13 n right d. 4.8 10-13 n left

The magnetic force is given as: F = qvBsinФ
where Ф is the angle between magnetic field (B) & the velocity of charge (v).

Since there is no Ф given, we assume, Ф = 90.
And we know, sin 90 = 1, we get, 
⇒ F = qvB
⇒ F = 1.6×10^(-19) C ×2.5×10^(7)×0.12 T
⇒ F = 0.48 × 10^(-12)
or F = 4.8 × 10^(-13)

Now, using flemingo's left hand rule to find the direction (right). 

Attached is the image.