Momentum and Its Conservation Chapter 9 Notes Momentum and Its Conservation

Section 9.1 Objectives Define the momentum of an object. Determine the impulse given to an object. Calculate the momentum and impulse of an object.

Momentum p = mv Units: kg*m/s

Practice Problems A 2250 kg pickup truck has a velocity of 25 m/s to the east. What is the momentum of the truck? What velocity must a 1210 kg car have in order to have the same momentum as the pickup truck in the previous problem?

Impulse and Momentum Recall Newton’s Second Law

Impulse FΔt

Impulse-Momentum Theorem FΔt = ρf – ρi Momentum and impulse are both vectors, so signs are important!!

Practice Problem A 2200 kg vehicle traveling at 26 m/s can be stopped in 21 s by gently applying the brakes. It can be stopped in 3.8 s if the driver slams on the brakes, or in 0.22 s if it hits a concrete wall. What average force is exerted on the vehicle in each of these stops?

Saving Lives with Impulse-Momentum Theorem What happens to the driver when a crash suddenly stops a car?

Section 9.2 Objectives Relate Newton’s third law to conservation of momentum in collisions.  Identify conditions that momentum is conserved.  Solve conservation of momentum problem.

Law of Conservation of Momentum pi = pf pi,A + pi,B = pf,A + pf.B

Conditions for Conservation of Momentum Closed system Isolated system

Conservation of Momentum

Practice Problem A 76 kg boater, initially at rest in a stationary 45 kg boat, steps out of the boat and onto the dock. If the boater moves out of the boat with a velocity of 2.5 m/s to the right, what is the final velocity of the boat?

Inelastic Collisions Example: meteorite collides head on with Earth, becoming buried in Earth mAvi + mBvi = (mA + mB)vf

Practice Problem A 1850 kg luxury sedan stopped at a traffic light is struck from the rear by a compact car with a mass of 975 kg. The two cars become entangled as a result of the collision. If the compact car was moving at a velocity of 22.0 m/s to the north before the collision, what is the velocity of the entangled mass after the collision?

Elastic Collisions

Practice Problem A 0.015 kg marble moving to the right at 0.225 m/s makes an elastic head on collision with a 0.030 kg shooter marble moving to the left at 0.180 m/s. After the collision, the smaller marble moves to the left at 0.315 m/s. Assume that neither marble rotates before or after the collision and that both marbles are moving on a frictionless surface. What is the velocity of the 0.030 kg marble after the collision?