A cannon is placed on a smooth surface. When it fires a shell, the cannon moves backward. This recoil occurs due to:
Correct answer: C. Newton's third law of motion
- 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.
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About Linear Momentum
Linear momentum is the vector product of mass and velocity, p = mv, and changes when a net external force acts. Work includes impulse as the change in momentum, conservation of momentum in isolated systems, collisions and explosions, and the distinction between elastic, inelastic and perfectly inelastic collisions.
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