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Lydia proposes to send an interstellar probe off in stages. The first stage, tra

ID: 1409203 • Letter: L

Question

Lydia proposes to send an interstellar probe off in stages. The first stage, traveling radially outward at 0.500 c relative to Earth, will send off a second stage traveling in the same direction as the first stage at a speed of 0.500 c relative to the first stage. Finally, the second stage will send off a third stage traveling in the same direction at 0.500 c relative to the second stage. Relative to Earth, the speed of the third stage will have a magnitude of:

a) 0.500c

b) 0.800c

c) 0.929c

d) 0.972c

e) 1.500c

I need help trying to understand this, and I'd prefer if there was some notation to the velocities so that I can better understand the order of progression for the answer.

Explanation / Answer

option c is correct

velocity of second stage wrt earth

v = (v’ + u)/(1 + v’u/c2 )

v = (c/2 + c/2)/(1 + (1/2)(1/2)) = 4c/5

velocity of third stage wrt earth,

v = (c/2 + 4c/5)/(1 + (1/2)(4/5)) = 0.929c

option c is correct

v' is the relative velocity of second stage with respect to first stage and u is the velocity of first stage (for first equation) ....this equation is used twice....the other time for second and third instead of first and second in equation