Name ______________________
Period ____ Date ___________
**Impulse and Momentum Notes**
**Momentum **is defined as **p ***= m***v***, *where **p **is the symbol for momentum, **m **is the symbol for mass, and **v **is the symbol for velocity. Momentum is a vector quantity and points in the direction of the direction of the velocity. Momentum has units of kg m/s. A large mass moving at a high velocity has a large momentum.
**Impulse **is defined as **J ***= ***F**_{av}* Δt, *where **J **is the impulse and **F**_{av}* *is the average force over an event (collision) over a time period *Δt*. The time interval is normally short, but that is not a real restriction. Impulse has the same units as momentum and, in normal usage, an impulse is given to an object producing a change in momentum. Thus, **J ***= mΔ***v **for an object involved in a collision type event.
**Conservation of Momentum **is a law regarding the total **momentum **of a system when external forces can be neglected. The most common use of this law is in describing features of collisions. The simplest of these events is a head on collision between two objects. In that situation, the **total momentum **of the colliding objects before the collision is equal to the **total momentum **after the collision. *m*_{1}*v*_{1}+*m*_{2}*v*_{2}* *= *m*_{1}*v*_{1}*’ *+ *m*_{2}*v*_{2}*’*
**Totally Elastic Collision **is a collision where kinetic energy is conserved. This is an ideal situation, because some kinetic energy is almost always lost in a collision.
**Totally Inelastic Collision **is a collision where the two (or more) colliding objects stick together after the collision. A significant amount of kinetic energy will be lost in this type collision.
**Example Using Impulse and Momentum Concepts - Answer the Questions Below.**
A 2 kg cart rolls across the floor, runs into the wall, and sticks. Before the collision, the cart has a velocity of 4 m/s in the x direction. The collision took place in 0.1 s. The **bold quantities **below are vectors and require a direction as part of the answer.
1. What was the cart’s **momentum **before the collision? ______________
2. What was the cart’s KE before the collision? ______________
3. What was the cart’s **momentum **after the collision? ________________
4. What was the change in the cart’s **momentum**? ________________
5. What was the **impulse **delivered to the car by the wall? ________________
6. What was the **average force **exerted on the car by the wall? _______________
7. What was the **average force **exerted on the wall by the car? _______________
8. Describe the collision as partially elastic, totally elastic, totally inelastic. ____________ |