Aim: How do we use conservation of momentum to solve explosion problems?

Defining an explosion In an explosion, an internal impulse acts in order to propel the parts of a system (often a single object) into a variety of directions. After the explosion, the individual parts of the system (that is often a collection of fragments from the original object) have momentum.

More on explosions If the vector sum of all individual parts of the system could be added together to determine the total momentum after the explosion, then it should be the same as the total momentum before the explosion. Just like in collisions, total system momentum is conserved.

Example of Explosion What is the total momentum of this system before the explosion? 0 kg m/s What is the total momentum of this system after the explosion? 0 kg m/s What must be the relationship between the momentum of the cannon-car system and the momentum of the tennis ball? The momentum of the cannon-car is equal and opposite to the momentum of the tennis ball

Another example of an explosion Why do both carts have equal momenta after the explosion occurs? Because their total momenta must add to zero Note: The total momentum of a system before and after an explosion is typically equal to 0

Explosion Conceptual Questions 1. Two pop cans are at rest on a stand. A firecracker is placed between the cans and lit. The firecracker explodes and exerts equal and opposite forces on the two cans. Assuming the system of two cans to be isolated, the post-explosion momentum of the system ____. is dependent upon the mass and velocities of the two cans b. is dependent upon the velocities of the two cans (but not their mass) c. is typically a very large value d. can be a positive, negative or zero value e. is definitely zero

Explosion Conceptual Questions 2. Two ice dancers are at rest on the ice, facing each other with their hands together. They push off on each other in order to set each other in motion. The subsequent momentum change (magnitude only) of the two skaters will be ____. greatest for the skater who is pushed upon with the greatest force b. greatest for the skater who pushes with the greatest force c. the same for each skater d. greatest for the skater with the most mass e. greatest for the skater with the least mass

Explosion Problems A 5.2 kg rocket shoots 0.89 kg of exhaust gas out of its engine with an average velocity of 755 m/s.   Compute the speed of the rocket. A 1.5 kg cart flies apart at 0.27 m/s from an explosion with a 4.5 kg cart.   What is the velocity of the 4.5 kg cart? An 80 kg camper jumps from a 45 kg canoe.   If the velocity of the camper is 4.0 m/s, what is the velocity of the canoe in the opposite direction?   Has this ever happened to you? A 225 kg cannon fires a 5.1 kg projectile with a muzzle velocity of 850 m/s.   Compute the recoil velocity of the cannon.