The cannon, subscript
In this case, all the motion is horizontal, so we can use a scalar quantity for the velocity.
It is often easy to measure and keep track of momentum, even with complicated systems of many objects. Consider a collision between two ice hockey pucks. The collision is so forceful that it breaks one of the pucks into two pieces. Kinetic energy is likely not conserved in the collision, but momentum will be conserved.
Provided we know the masses and velocities of all the pieces just after the collision, we can still use conservation of momentum to understand the situation. This is interesting because by contrast, it would be virtually impossible to use conservation of energy in this situation. It would be very difficult to work out exactly how much work was done in breaking the puck.
- Collisions with "immovable" objects are interesting. Of course, no object is really immovable, but some are so heavy that they appear to be. Consider the case of a bouncy ball of mass
If momentum is conserved, then the momentum of the earth and wall also must have changed by
What kind of problems can we solve using momentum conservation?
Exercise 1a: The recoil of a cannon is probably familiar to anyone who has watched pirate movies. This is a classic problem in momentum conservation. Consider a wheeled, 500 kg cannon firing a 2 kg cannonball horizontally from a ship. The ball leaves the cannon traveling at 200 m/s. At what speed does the cannon recoil as a result?
Exercise 1b: Suppose the cannon was raised to fire at an angle
Exercise 2a: A golf club head of mass
