1. The problem statement, all variables and given/known data I have a 1g object on a frictionless surface being hit with light of a frequency 632nm (directly parrallel to the surface and the object absorbs all the light). How many photons did the object absorb by the time it's moving at 1mm/s? 2. Relevant equations 3. The attempt at a solution Well I worked it out two different ways and I got two different answers: My first attempt is via conservation of energy: n*h*c/lambda + m*c^2 = gamma*m*c^2 where n is the number of photons h is planck's constant c is the speed of light lambda is the wavelength m is the mass of the object gamma is the 1/sqrt(1-v^2/c^2) Then I solved for n. My second attempt is via conservation of momentum: n*h/lambda = gamma*m*v Then I solved for n. In both cases I got different answers. So I'm not sure what's wrong.