Chapter 9 Momentum & Its Conservation

Chapter 9 Momentum & Its Conservation

9.1 Impulse & Momentum Momentum is a vector quantity That is defined as the product Of an object’s mass and velocity. p = mv

Problem... A 2250 kg pickup truck has a Velocity of 25 m/s to the east. What is the momentum of The truck? 56250 kg m/s

Problem... A 21 kg child is riding on a 5.9 kg Bike with a velocity of 4.5 m/s To the north west. What is the Total momentum of the child & bike Together? Just the child? Just The bike? 120 kg m/s 94 kg m/s 27 kg m/s

A change in momentum Takes force and time. The Impulse-Momentum Theorem FΔt = Δp or FΔt = mvf - mvi

Impulse (for a constant external Force) is the product of the Force and the time over which It acts on an object. FΔt is called the Impulse.

Problem... A 1400 kg car moving westward With a velocity of 15 m/s Collides with a utility pole. It is then Brought to a stop in 0.30s. Find The magnitude of the force Exerted on the car during the Collision. 7 X 104N

Stopping times and distances Depend on the impulse- Momentum theorem. A change in momentum over A longer time requires less force.

Angular momentum is the product Of a rotating object’s moment Of inertia and angular Speed about the same axis. L = Iω

Problem... Erica, 65kg, is spinning on a merry- Go-round that has a mass of 115kg, And a radius of 2m. She walks From the edge to the center. If The angular speed is initially 2 rad/s What is its angular speed when she Reaches a point 0.5m from The center? 3.9 rad/s

The angular impulse-momentum Theorem states that the angular Impulse on an object is equal To the change in the object’s Angular momentum. τΔt = Lf - Li

9.2 Conservation of Momentum The total momentum of all objects Interacting with one another Remains constant regardless of The nature of the forces Between the objects.

The conservation of momentum Can be shown as a formula… m1v1i + m2v2i = m1v1f + m2v2f Momentum is conserved in Collisions and for objects Pushing away from each other.

Problem... A 76 kg boater (Charlie), initially At rest in a stationary 45 kg boat, Steps out of the boat and onto the Dock. If Ryan moves out of the Boat with a velocity of 2.5 m/s, What is the final velocity Of his boat? v2f = 4.2 m/s

Problem... An 85 kg fisherman jumps from a Dock into a 135 kg rowboat at rest On the west side of the dock. If the Velocity of the fisherman is 4.3 m/s to the west, what is the Final velocity of the Fisherman and the boat? 1.66 m/s to the west

Elastic & Inelastic Collisions There are two kinds of collisions: Those that bounce off of each other And those that stick together

A perfectly inelastic collision is a Collision in which two objects Stick together and move with A common velocity after Colliding. The formula for a perfectly Inelastic collision m1v1i + m2v2i = (m1 +m2) vf

Problem... An 1850 kg Cadillac stopped at a Light is struck from the rear by A Honda with a mass of 975 kg. The 2 cars become entangled. If the Honda was moving at 22 m/s to the north before, what Is the velocity of the entangled Mess after the collision? vf = 7.59 m/s to the north

Problem... A grocery shopper tosses a 9 kg Bag of dog food into a stationary 18 kg cart. The bag hits the cart With a horizontal speed of 5.5 m/s Toward the front of the cart. What is the final speed of the Cart and bag? 1.8 m/s

The law of conservation of Angular momentum states that If no external torque acts on an Object, then its angular momentum Does not change. L1 = L2 Iω = Iω

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Chapter 9 Momentum & Its Conservation