PhysicsLAB AP Free Response Question
2009 Form B - B2

 
 
Three particles are arranged on coordinate axes as shown above. Particle A has charge qA = -0.20 nC , and is initially on the y-axis at y = 0.030 m. The other two particles each have charge qB = +0.30 nC and are held fixed on the x-axis at x = -0.040 meters and x = +0.040 meters, respectively.
 
 (a) Calculate the magnitude of the net electric force on particle A when it is at y = 0.030 m, and state its direction.

 (b) Particle A is then released from rest. Qualitatively describe its motion over a long time.

In another experiment, particle A of charge qA = -0.20 nC is injected into a uniform magnetic field of strength 0.50 T directed into the page, as shown below, entering the field with speed 6000 m/s.
 
 
 (c) On the diagram above, sketch a complete path of particle A as it moves in the magnetic field.

 (d) Calculate the magnitude of the force the magnetic field exerts on particle A as it enters the magnetic field.

 (e) An electric field can be applied to keep particle A moving in a straight line through the magnetic field. Calculate the magnitude of this electric field and state its direction.





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