A train travels 55 km south along a straight track in 34 minutes. What is the train's average velocity in kilometers per hour?
2 answers:
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(a) The electrons move horizontally from west to east, while the magnetic field is directed downward, toward the surface. We can determine the direction of the force on the electron by using the right-hand rule:
- index finger: velocity --> due east
- middle finger: magnetic field --> downward
- thumb: force --> due north
However, we have to take into account that the electron has negative charge, therefore we have to take the opposite direction: so, the magnetic force is directed southwards, and the electrons are deflected due south.
b) From the kinetic energy of the electrons, we can find their velocity by using
where K is the kinetic energy, m the electron mass and v their velocity. Re-arranging the formula, we find
The Lorentz force due to the magnetic field provides the centripetal force that deflects the electrons:
where
q is the electron charge
v is the speed
B is the magnetic field strength
m is the electron mass
r is the radius of the trajectory
By re-arranging the equation, we find the radius r:
And finally we can calculate the centripetal acceleration, given by:
- index finger: velocity --> due east
- middle finger: magnetic field --> downward
- thumb: force --> due north
However, we have to take into account that the electron has negative charge, therefore we have to take the opposite direction: so, the magnetic force is directed southwards, and the electrons are deflected due south.
b) From the kinetic energy of the electrons, we can find their velocity by using
where K is the kinetic energy, m the electron mass and v their velocity. Re-arranging the formula, we find
The Lorentz force due to the magnetic field provides the centripetal force that deflects the electrons:
where
q is the electron charge
v is the speed
B is the magnetic field strength
m is the electron mass
r is the radius of the trajectory
By re-arranging the equation, we find the radius r:
And finally we can calculate the centripetal acceleration, given by: