Question

A positively charged croquet ball rolls at $4.0m/s$ northward through a $2.00T$ magnetic field which points westward.
If the charge on the croquet ball is $1.0C$, how much force acts on the croquet ball due to the magnetic field and in what direction?

• A. Amount of Force - $2.00N$, Direction of Force - up
• B. Amount of Force - $8.00N$, Direction of Force - south
• C. Amount of Force - $8.00N$, Direction of Force - down
• D. Amount of Force - $0.500N$, Direction of Force - up
• E. Amount of Force - $8.00N$, Direction of Force - up

Answer 1

The correct option is E Amount of Force - $8.00N$, Direction of Force - up

From figure, $\overrightarrow{v}=-4.0$ $\hat{z}$ $\overrightarrow{B}=-2.00$ $\hat{x}$ $q=1.0$ C

Magnetic force on the ball $\overrightarrow{F}=q(\overrightarrow{v}\times \overrightarrow{B})$

$\therefore$ $\overrightarrow{F}=1.0\left[\right(-4.0)\hat{z}\times (-2.00\left)\hat{x}\right]=8.00$ $\hat{y}$

Thus magnetic force of $8.00$ $N$ acts in the upward direction.