Worldlines

E2. On the spacetime diagram at right draw the following worldlines:

A. Object at rest at the origin O.

B. Object moving to the right through O at 1/2 c.

C. Object moving to the left through O at 1/2 c.

D. Object moving to the right through O at 0.8 c.

E. Object moving to the left through O at 0.8 c.

F. Photon moving to the right through O at c.

G. Photon moving to the left through O at c.

H. Object at rest at x = 3 cy.

I. Object starting at rest at x = 1 cy when t = 0 and which accelerates smoothly to the right so as just to stay ahead of photon F.

How fast is D going with respect to B?