MHB Multiple choice question about electric fields and magnetic fields

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In a region with a 25-volt-per-meter electric field and a 15-millitesla magnetic field, an electron moves at a 20-degree angle relative to the magnetic field, experiencing a force of 5 × 10^-18 Newtons. The Lorentz force equation is applied to analyze the situation, combining the effects of the electric and magnetic fields. The relationship between the force, electric field, magnetic field, and electron speed is established through the equation F = -e(E + v × B). By substituting the known values into the derived formula for speed, the calculation yields the electron's velocity. The correct speed of the electron is determined to be 10.46 km/s.
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Consider a region where a 25-volt-per-meter electric field and a 15-millitesla magnetic field exist and are along the same direction. If the electron is in the said region, is moving at a direction 20 degrees counter-clockwise from the direction of the magnetic field, and is experiencing a total force of 5 × 10-18 Newtons, determine the speed of the electron. Assume the velocity vector, the electric field, and the magnetic field are all lying on the same plane.

a.) 10.46 km/s
b.) 1.32 km/s
c.) 3.65 km/s
d.) 5.20 km/s
 
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By the Lorentz law, the electromagnetic force is given by $\mathbf{F} = -e(\mathbf{E} + \mathbf{v} \times \mathbf{B})$, where $e$ is the elementary charge, equal to $1.6 \times 10^{-19} C$. Since the electric and magnetic fields point in the same direction, we may suppose that they are in the $x$-direction. Then $\mathbf{v} \times \mathbf{B}$ points in the negative z-direction and has magnitude $vB\sin(20^\circ)$. Therefore $\mathbf{F} = -e(E\,\mathbf{\hat{x}} - vB\sin(20^\circ)\,\mathbf{\hat{z}})$. Taking the square of the magnitude on both sides of the vector equation yields $F^2 = e^2[E^2 + (vB \sin 20^\circ)^2]$. Solving for $v$ results in $$v = \frac1{B\sin20^\circ}\sqrt{\left(\frac{F}{e}\right)^2 - E^2}$$ Plug in the given values of $F$, $E$ and $B$ into this formula to determine the answer.
 
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