Physics problems?

[football god]

Need a lil help on these questions
1. A 7600kg space probe is traveling through space at 120 m/s. Mission control determines that a change in course of 30.0° is necessary and, by electronic communication, instructs the probe to fire its rockets perpendicular to its present direction of motion. If the escaping gas leaves the craft’s rockets at 3200 m/s, what mass of gas should be expelled?
2. Which collision presents the greater possibility of danger to the passengers involved (1) two cars colliding and remaining entangled, or (2) the same two cars colliding and rebounding off each other? Explain.
3. A spacecraft in outer space increases its velocity by firing its rockets. How can hot gasses escaping from rockets change the velocity of the craft when there is nothing in space for the gasses to push against?
4. When you shoot a riffle for the first time, you quickly learn to place the butt of the riffle firmly against your shoulder. In terms of momentum, why is this good advice?