#### Transcript Impulse and Momentum

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 P = Mv High velocity bullet 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. F Dt Minimize the Force Increase Dt Catching a ball Bungee jumping Dt F Maximize Momentum Change Apply a force for a short time. Examples: Boxing Karate F Dt Conservation of Momentum This means that the momentum doesn’t change. Internal forces cannot cause a change in momentum. Collisions Before v2 m1 m2 v1 After m1 v2 m2 m1v1 m2 v2 m1v1 m2 v2 v = 10 v=0 M M Before Collision p = Mv v’ = 5 M M Mv = 2Mv’ v’ = ½ v After Collision p = 2Mv’ Conserve Energy and Momentum Before Collision Case 1: Equal masses 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 m1v1 m2 v2 m1v1 m2 v2 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?