Chapter 12: Q12.38P (page 549)
Show that it is possible to outrun a light ray, if you're given a sufficient head start, and your feet generate a constant force.
Short Answer
It is possible to outrun a light ray.
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Chapter 12: Q12.38P (page 549)
Show that it is possible to outrun a light ray, if you're given a sufficient head start, and your feet generate a constant force.
It is possible to outrun a light ray.
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鈥淚n a certain inertial frame S, the electric field E and the magnetic field B are neither parallel nor perpendicular, at a particular space-time point. Show that in a different inertial system , moving relative to S with velocity v given by
the fieldsare parallel at that point. Is there a frame in which the two are perpendicular?
The coordinates of event Aare and the coordinates of event B are. Assuming the displacement between them is spacelike, find the velocity of the system in which they are simultaneous.
Check Eq. 12.29, using Eq. 12.27. [This only proves the invariance of the scalar product for transformations along the x direction. But the scalar product is also invariant under rotations, since the first term is not affected at all, and the last three constitute the three-dimensional dot product a-b . By a suitable rotation, the x direction can be aimed any way you please, so the four-dimensional scalar product is actually invariant under arbitrary Lorentz transformations.]
Inertial system moves in the direction at speed relative to system. (Theaxis slides long theaxis, and the origins coincide at , as usual.)
(a) On graph paper set up a Cartesian coordinate system with axesrole="math" localid="1658292305346" and . Carefully draw in lines representingand. Also draw in the lines corresponding to , and. Label your lines clearly.
(b) In, a free particle is observed to travel from the point at timeto the point at. Indicate this displacement on your graph. From the slope of this line, determine the particle's speed in .
(c) Use the velocity addition rule to determine the velocity in algebraically,and check that your answer is consistent with the graphical solution in (b).
A cop pulls you over and asks what speed you were going. 鈥淲ell, officer, I cannot tell a lie: the speedometer read .鈥 He gives you a ticket, because the speed limit on this highway is . In court, your lawyer (who, luckily, has studied physics) points out that a car鈥檚 speedometer measures proper velocity, whereas the speed limit is ordinary velocity. Guilty, or innocent?
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