Question

An upward force acts on a proton as it moves with a speed of 2.0 × 105 meters/second through a magnetic field of 8.5 × 10-2 tesla running from east to west. What is the force and direction of the force on the proton?
2.7 × 10-15 N to the north
2.7 × 10-15 N to the south
1.7 × 10-14 N to the north
1.7 × 10-14 N to the south
1.7 × 10-14 N downward

Answer 1

We are given:

the speed of a proton = 2.0 × 10^5 meters/second; 
moving through a magnetic field = 8.5 × 10-2 tesla 
direction: east to west

The force and the direction of the force of the proton is determined using the magnetic field formula

F = qvxB

where q = charge 
v = vector
x = speed
B = magnetic field


F = 1.6x10^-19 C * 2.0 × 10^5 m/s * 8.5 × 10-^2 tesla

solve for F and the direction of your force is opposite the direction of the proton which is north since the proton is going upwards. 

Answer 2

Explanation :

It is given that,

Speed of the proton, $v=2\times 10^{5}\ m/s$

Magnetic field, $B=8.5\times 10^{-2}\ T$

Magnetic force is given by :

$F=q(v\times B)$

q is the charge of proton, $q=1.6\times 10^{-19}\ C$

So,

$F=1.6\times 10^{-19}\ C\times 2\times 10^{5}\ m/s\times 8.5\times 10^{-2}\ T$

$F=2.72\times 10^{-15}\ N$

The direction of force is given by using right hand rule. So, the force will act in upward direction.

Hence, the correct option is (a) " $2.72\times 10^{-15}\ N$ to the north".