By conservation of momentum, the initial recoil speed of the
rifle is:
u = 904kg * 0.0106 kg / 3.53 kg = 2.7146 m/s
The final recoil speed v is zero in a distance of d = 0.0346 m
So the rifle's acceleration is a = (0 - u^2) / 2*d = -2.7146^2 / 2*.0323
m/s^2
a = -114.07m/s^2
