1. Chapter 6 Momentum and Impulse

2. Momentum The product of an object’s mass and velocity: p = mv Momentum, p, and velocity, v, are vector quantities, meaning they have magnitude and direction. The units for momentum are kg * m /s.

3. Momentum Examples… A 61-kg man is traveling north in a 3200- kg car at 15 m/s. What is the momentum of the man? What is the momentum of the car? What is the total momentum of the man and car together? How fast must an 11,000-kg truck travel to have the same momentum as the man and the car in the previous problem?

4. Impulse Since a net external force changes the velocity of an object, it also changes the object’s momentum. If a net external force, F, is applied to an object for a certain time interval, Δt, then FΔt is the impulse of the force. Impulse equals the object’s change in momentum. FΔt = Δp or FΔt = mv f - mv i

5. Force and Momentum Examples A 145-gram baseball is thrown to the right at 17 m/s. The first baseman catches the ball and brings it to rest in 0.013 s. What force does the first baseman exert on the ball? A 7.1-kg piece of wood is dropped from a cliff 83 meters above the ocean. What is the velocity of the wood when it hits the water? If the water exerts an upward force of 140 N on the piece of wood, how long will it take for the piece of wood to come to a stop?

6. Stopping Distance Examples A 3200-kg car is traveling east at 14 m/s when the driver steps on the brake pedal. The brakes apply a force of 9400 N to the west. How far does the car travel before it comes to a stop? In the previous problem, what is the car’s velocity 1.0 second after the brakes are applied? How far has it traveled after 1.0 second? 560 kg of cargo is loaded into the back of the car in the previous problem. If the same brake force is applied, how long will it take the car to come to a stop and how far will it go?

7. Conservation of Momentum The total momentum of two interacting objects remains constant (friction is disregarded): m 1 v 1,i + m 2 v 2,i = m 1 v 1,f + m 2 v 2,f

8. Conservation of Momentum Examples A 72-kg man jumps off of a 327-kg boat that is at rest. His velocity is 3.8 m/s to the east. What is the velocity of the boat after the man’s jump? A cue ball and the 8-ball both have a mass of 160 g. The cue ball is traveling 1.3 m/s when it strikes the 8-ball, which is initially at rest. What is the final speed of the 8-ball if the final speed of the cue ball is 0.5 m/s in the same direction? A baseball player swings a 0.95-kg bat to hit a 145-gram baseball. The speed of the bat is 15 m/s before hitting the ball and 11 m/s after. What is the velocity of the baseball immediately after impact?