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Relativistic momentum

QUESTION: A proton has a rest mass of 1.673 x 10-27 kg. If it is accelerated to a speed of 0.93c what is the magnitude of the relativistic momentum of proton?
Possible answers:
(a) 6.2 x 10-17 kg m/s
(b) 1.3 x 10-18 kg m/s
(c) 4.7 x 10-19 kg m/s
(d) 5.9 x 10-24 kg m/s
(e) 1.6 x 10-27 kg m/s


Momentum (p) = mv/(1 v2/c2)1/2
if the velocity is given as 0.93c then the "c" within the denominator will cancel leaving:

p = m0.93c/[1 - 0.932]1/2

Notice that you still have a "c" in the numerator!

Substituting the values for m and c gives:

Relativistic momentum of the proton = 1.3x10-18 kg m/s.

The correct answer is (b).
© Keith Gibbs 2011