Chapter 7 Linear Momentum

Important Concepts

a.) F = Dp/Dt and the definition of momentum: p = mv

b.) Conservation of momentum in an isolated system (Fnet = 0) . Total Momentum is conserved.

c.) Collisions

Inelastic: Objects stick or there is an explosion that blows them apart. Momentum is conserved, but total kinetic energy is not.

Elastic: Objects bounce off each other. Momentum is conserved and total Kinetic Energy is conserved.

Required:

Questions: 4,6,

Problems: 2, 7, 26, Dr. H. Reality Check, Reality Check

Dr. H Reality Check Accident Reconstruction: A drunk driver rear ends a vehicle stopped at a red light. As the reporting officer you note that both cars are essentially fused together. To compile a police report you record the following information. A Dodge Neon (mass = 1000 kg) was rear ended by a Cadillac Eldorado (mass = 2000 kg). The skid marks from the point where the cars made contact to the point where they both came to rest are 10 meters long. It is a cool night and the pavement is dry, so there is good friction between the tires and the road. The drunk driver is already getting a handful of tickets: OWI, running a red light, driving with a suspended licensee, and causing an accident. You would like to throw in a speeding ticket for good measure. The posted speed limit is 40 mph. If you issue a speeding ticket, will it stand up in court based on the facts or will it be dismissed.

Suggested:

Questions: 1, 2, 5, 7, 11, 14

Problems: 4, 8, 32, 36a,b, 66

Answers

2. 0.72 m/s

8. 507 m/s

26. 3.62 m/s, 4.42 m/s b.)-396 kg m/s and +396 kg m/s

32. large 3000 J

small 4500 J

36 a.) 1.93 m/s

b.) 7.8 m/s, -1.6 m/s

50. x cm = 1.2 L from the left

y cm = 2.1 L from the front

66 a.) –0.194 m/s (+/- depends on how set up the problem)

b.) +/- 700 Newtons