Time Space Diagram: Is Object B Moving Along x-Axis?

[questions]

i attached the diagram.

a) the object whose world line is labeled B is moving along the x-axis T or F?

I said false because yes while it is moving along the x-axis it's also moving along the y-axis. So it's moving in two dimensions not just one. is my answer and reasoning correct?
The world line for object E (a completely horizontal world line) cannot possibly be correct right? The reason behind this is because it has a slope of zero and it must have a slope of one or greater. Having a slope of 1 or less than one means that the object is traveling at the speed of light or faster than the speed of light which is not possible.

 

[Doc Al]

i attached the diagram.

a) the object whose world line is labeled B is moving along the x-axis T or F?

I said false because yes while it is moving along the x-axis it's also moving along the y-axis. So it's moving in two dimensions not just one. is my answer and reasoning correct?

No, your answer is incorrect. For one thing, the "y-axis" represents time. The spacetime diagram is just a picture representing where the object is as a function of time. World line B shows an object moving left and then right along the x-axis.

The world line for object E (a completely horizontal world line) cannot possibly be correct right? The reason behind this is because it has a slope of zero and it must have a slope of one or greater. Having a slope of 1 or less than one means that the object is traveling at the speed of light or faster than the speed of light which is not possible.

Right! (Assuming you are measuring both axes with comparable units--ct instead of just time.)

 

[questions]

for the first portion.

if the object is moving left then right along the right-axis then what is the difference of an object that is moving in a curved manner like B and an object that would move in a staright manner like A

 

[Doc Al]

While the worldline of B might be curved, both A and B are moving in a straight line. They both only move back and forth along the x-axis. The difference is that A moves with constant speed to the left then instantly reverses direction and moves with constant speed to the right while B slows down and reverses direction more gently.