7. A 1400-kg cannon, which fires a 70.0-kg shell with a muzzle speed of 556 m/s, is set at an elevation angle of 39.0° above the horizontal.
The cannon is mounted on frictionless rails, so that it recoils freely.
(a) What is the speed of the shell with respect to the Earth?
(b) At what angle with the ground is the shell projected?
(Hint: The horizontal component of the momentum of the system remains unchanged as the gun is fired.)