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# How do I find the speed of an object relative to another object traveling away from it?

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How do I find the speed of an object relative to another object traveling away from it?

Guest Aug 27, 2015

#3
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How do I find the speed of an object relative to another object traveling away from it?

If the 2 speeds are   6km/h and 4 km/h     then the relative speed will be  10km/h

This is simplistic but I think it is correct.   :)

Melody  Aug 28, 2015
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#1
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i think it may be the answer you have questened.the answer must be checked.......

Velocities are strange beasts. Relativity theory tells us rapidities (the sum of the accelerations experienced by an object) are more intuitive quantities. Rapidities are directly observable quantities (external observers relate these to blue/redshifts). And unlike velocities, rapidities do sum up. Velocities depend non-linearly on rapidities, and therefore velocities follow a more complex addition rule.

Imagine three observers AB and C all moving along a railway track. Observer A measures B to have velocity vAB. From B's perspective C has a velocity vBC. And to close the circle, from C's perspective A has velocity vCA.

Common experience (encoded in so-called Galilean relativity) tells us these velocities simply add up to zero:

vAB+vBC+vCA=0

This is wrong. It ignores a non-linear term that becomes important at speeds approaching the speed of light c. Lorentzian relativity tells us the correct equation is:

vAB+vBC+vCA+vAB.vBC.vCA/c2=0

This is all the math you need. Give it a try. Enter vAB=0.9c and vBC=0.9c and see what value you get for vAC=vCA.

matsunnymat  Aug 27, 2015
#2
+5

How do I find the speed of an object relative to another object traveling away from it?

First, you have to time it by a clock, or know the time travelled.

Second, you have to measure,or know, the distance travelled.

Speed=Distance/Time

Guest Aug 27, 2015
#3
+91409
+5

How do I find the speed of an object relative to another object traveling away from it?

If the 2 speeds are   6km/h and 4 km/h     then the relative speed will be  10km/h

This is simplistic but I think it is correct.   :)

Melody  Aug 28, 2015
#4
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Guest Sep 11, 2015

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