T or F: Magnetism and Magnetic Field

[choco_moo]

Homework Statement

A 2 kg particle carrying a charge of 97 uC enters a uniform 7 T magnetic field at a speed of 26 m/s and with an angle of 52o with respect to the field lines, as shown in the figure. Answer the following questions:

A) The work done by the field on the particle is zero as the force is normal to the displacement.
B) The y-component of the particle's velocity is unchanged as it passes through the B-Field.
C) The Force on the particle is in the -z direction.
D) The particle follows a circular path as the force is normal to the velocity.
E) The particle's speed is unchanged as it passes through the B-Field.

The Attempt at a Solution

A) The work done by the field on the particle is zero as the force is normal to the displacement.T but I'm not sure.
B) The y-component of the particle's velocity is unchanged as it passes through the B-Field.F because the field lines are perpendicular to the y-component. Parallel components remain unchanged.
C) The Force on the particle is in the -z direction.No idea
D) The particle follows a circular path as the force is normal to the velocity.No idea
E) The particle's speed is unchanged as it passes through the B-Field.T because B can only change the direction of the velocity.

Any help is much appreciated!

 

[willem2]

How do you find the direction of the force, if you know the direction of the field and the direction of the velocity of the particle? You need this for A and C

for D, look at your answer for B (which is correct)
How can you answer E be not sure about A?

 

[choco_moo]

How do you find the direction of the force, if you know the direction of the field and the direction of the velocity of the particle? You need this for A and C

for D, look at your answer for B (which is correct)
How can you answer E be not sure about A?

I don't know. I assume I have to use the right hand rule, but I don't get how that works. The particle is moving through the field at 52 degrees, but work is zero if the displacement and force are perpendicular to each other. I don't see how work can be zero because isn't the displacement going to be 52 degrees on every line? I am so confused.

 

[willem2]

I don't know. I assume I have to use the right hand rule, but I don't get how that works. The particle is moving through the field at 52 degrees, but work is zero if the displacement and force are perpendicular to each other. I don't see how work can be zero because isn't the displacement going to be 52 degrees on every line? I am so confused.

Whatever the angle of the field and the velocity, it's always possible to have a
force that's perpendicular to both.

 

[choco_moo]

Whatever the angle of the field and the velocity, it's always possible to have a
force that's perpendicular to both.

So I figured out the answers:
A) True, because of what you just stated.
B) False, because the direction is always changing. The B-field is constantly moving.
C) True, because of the right hand rule. -z is pointing into the page.
D) False, because the B-field is always moving, so the particle would follow a spiral-like shape instead of circular.
E) True, because if work is zero then speed can not change.

Thanks for the help!

 

[willem2]

The B field isn't moving
but the direction of the force on the particle is.

The particle follows a spiral and not a circle, because the x component of its velocity is in the direction of the B field and the force on the particle can't have a component in the x direction, so the x component of the velocity can't change.