Hello all,(adsbygoogle = window.adsbygoogle || []).push({});

I got this question off mastering physics and was unable to understand it. I eventually gave up to concentrate on other assignments and asked for the answer. I was unable to come up with more than one answer I thought possible without resorting to trial and error.

Answer: V_{x},V_{y},V_{z}= 0,-234,0 m/s

1. The problem statement, all variables and given/known data

A 6.50 negative microC particle moves through a region of space where an electric field of magnitude 1200 N/C points in the positive x direction, and a magnetic field of magnitude 1.02 T points in the positive z direction.

If the net force acting on the particle is 6.25×10^{−3 }N in the positive x direction, find the components of the particle's velocity. Assume the particle's velocity is in the x-y plane.

V_{x}= ? V_{y}=? V_{z}= ?

2. Relevant equations

Force = electric field * charge

or F=e*q

Force = magnitude of charge * velocity * magnetic field * sin tither

or F=|q|*v*B*sin tither

3. The attempt at a solution

Force on particle due to Electric Field = E*q

= (1200N/C)(-6.5*10^{-3}C)

= -7.8*10^{-3}N

Force on charge due to magnetic field = |q|*v*B*sin tither

= (6.5*10^{-6}C)(1.02T)(v)(sin 90)

= (6.63*10^{-6})(v)

F_{x1}along x axis = -7.8*10^{3}N

I'm sure the force on charge due to magnetic field lies between axis of positive Y and axis of negative X. The force on the particle needs to be perpendicular to the positive z direction of the magnetic field and the velocity of the particle which is one the x-y plane. Since the net force is in the x-direction, it should be along the x-axis. This was also the reasoning that led me to using sin90 when determining the force on the charge due to the magnetic field.

F_{x2}along x axis = (6.63*10^{-6})(v)

At this point, I thought I understood the problem statement fully. I took the net force from these two vectors I had come up with and seperated velocity to LHS and the constants to the right.

V_{x}= (Net Force x + F_{x1}) / (F_{x2}without velocity term)

= ((6.25×10^{−3 })+(7.8*10^{3})) / (6.63*10^{-6})

= 2.12*10^{7}m/s

The value was ridiculously large and I was not surprised it was rejected by mastering physics. I think I have a huge misunderstanding of the concept or method behind this question. Please explain to me how I should go about dealing with a question of this type or point out my mistakes. I do not need a worked out solution, coming up with that myself would probably be better for me.

Thank you

**Physics Forums | Science Articles, Homework Help, Discussion**

Join Physics Forums Today!

The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

# Homework Help: Initial velocity of a charged particle acted upon by magnetic and electric fields

**Physics Forums | Science Articles, Homework Help, Discussion**