A cannon is placed on a smooth surface. When it fires a shell, the cannon moves backward. This recoil occurs due to:
- A. Law of conservation of energy
- B. Backward thrust of the gases
- C. Newton's third law of motion
- D. Newton's first law of motion
Explanation
The cannon pushes the shell forward and the shell pushes the cannon back with an equal and opposite force, which is the third law, and the same situation expressed as conservation of momentum gives the recoil velocity. Because the cannon is far more massive than the shell, its backward speed is correspondingly small. Energy is conserved too, but it does not by itself explain the direction of the motion.