Suppose a spacecraft of rest mass 34000 kg is accelerated to 0.206c. How much kinetic energy would it have?


If you used the classical formula for KE, by what percentage would you be in error? Do not enter units.

1 answer

The exact relativistic KE is
mc^2*[1/sqrt[(1 -(v/c)^2] - 1]
= 3.4*10^5*(3.00*10^8)^2*(1.02192-1)
= 6.71*10^20 J
The nonrelativistic (classical) KE is
(1/2)M V^2 = (1/2)*(3.4*10^5)(6.18*10^7)^2 = 6.49*10^20
The percent error (relative to the correct value) is -3.1%