A cannon of mass 500 kg is mounted on frictionless horizontal rails. It fires a 2.0 kg shell with a muzzle speed of 400 m s⁻¹ at an angle of 60° above the horizontal. Find the speed with which the cannon rolls backward immediately after firing.
a) 1.6m s−1
b) 0.40m s−1
c) 0.80m s−1
d) 1.4m s−1