Impulse and Momentum

Momentum and Collisions The goal with lesson is to understand inertia and motion. Momentum helps us understand collisions. Elastic Collisions - objects rebound Inelastic Collisions - object stick together an usually become distorted and generate heat

Momentum Momentum = mass ´ velocity p = mv Momentum is a vector quantity.

Large Momentum Examples Huge ship moving at a small velocity High velocity bullet P = Mv P = mv

Momentum Examples A large truck has more momentum than a car moving at the same speed because it has a greater mass. Which is more difficult to slow down? The car or the large truck?

Impulse Newton’s Second Law can read F = ma F = m(Dv÷Dt) F = (Dmv)÷(Dt) F· ∆t = (Dp) ÷(∆t) ∙∆t Impulse (∆p)=FDt

When Force is Limited Apply a force for a long time. Examples: Follow through on a golf swing. Pushing a car. FDt

Minimize the Force Increase Dt Catching a ball Bungee jumping FDt

Maximize Momentum Change Apply a force for a short time. Examples: Boxing Karate FDt

Conservation of Momentum This means that the momentum doesn’t change. Internal forces cannot cause a change in momentum.

Collisions Before m2 m1 After m1 m2

Inelastic Collisions v = 10 v = 0 M M Before Collision p = Mv v’ = 5 M After Collision p = 2Mv’ Mv = 2Mv’ v’ = ½ v

Elastic Collisions Conserve Energy and Momentum Before Collision Equal masses Case 1: Case 2: M > M Case 3: M < M

Things I Understand… I Need to Know more of…

Conservation in Momentum 1. A 12,000kg. railroad car is traveling at 2m/s when it strikes another 10,000kg.railroad car that is at rest. If the cars lock together, what is the final velocity of the two railroad cars?  2. A 9,300 kg. railroad car traveling at a velocity of 15m/s strikes a second  boxcar at rest. If the two cars stick together and move off with a velocity of 6m/s, what is the mass of the second car? 3. A 25 gram bullet is fired from a gun with a speed of 230m/s. If the gun has a mass of 0. 9kg. What is the recoil speed of the gun? 4. A 20 gram bullet traveling at 250m/s strikes a block of wood that weighs 2kg. With what velocity will the block and bullet move after the collision? Conservation in Momentum

Impulse Impulse=FDt A rocket engine fires for 10 seconds while providing 4,000 N of thrust. What impulse is given to the rocket by its engines? A 500-g baseball is given an impulse of 12.5 N-s by a baseball bat. The bat is only in contact with the ball for 0.10 seconds. What is the average force of the bat acting on the ball?