Chapter 3 Answers:
Review Questions:
1. The moving skateboard hasy more momentum since the momentum of the truck is zero.
5. Yes: force is equal to impulse divided by the time (duration of the force). Since F=ma also (Newton's 2nd law), the two are related: F=ma=(Pf-Pi)/t
9. 'Rolling with the punch' increases the time of contact between the opponents glove and your face, decreasing the force of the punch.
13. No: because of Newton's third law, there will be at least two action-reaction pairs of force. The first (push on the dashboard/ it pushes back) will be cancelled out by the reaction force of the seat pushing forward on your back. These two reaction forces are equal as long as you stay at rest relative to the car by Newton's first law. Thus they cancel out, and the net outside force on the car is zero.
17. In both!
21. Work; It changes the kinetic energy of an object.
27. Four times as much
31. Energy is neither created or destroyed but may only change form in any interaction.
Exercises:
1. The 'crumple' zone increases the time of any collision, minimizing the force of the collision.
2. There is a typo in the problem. They must have intended the problem to read '...cut off 25 km from port'. The answer is that the supertanker has such an enormous inertia that even small accelerations require a huge amount of force. The large force of water resistance on the tanker would take miles to decelerate it to rest.
4. The time of collision on the concrete floor is much shorter than on the carpet. Therefore the force is much less.
6. It would require more stopping force if its initial velocity were large enough.
9. The looser the decoupling, the longer collisions between cars take, the smaller the force of these collisions. This reduces the likelihood of accidents and increases the lifetime of the hardware.
12. Due to conservation of momentum, the hose-firefighter system has to have the same momentum (in the opposite direction) as does the water. This causes a large force on the firefighter equal to the mass ejected per unit time multiplied by the speed of that mass of water. This is analogous to the reaction force from a gun (the 'kick'). The difference is that the mass ejected per unit time is larger in the case of the firehose though the velocity of the water iss much less than that of a typical bullet.
20. The smaller 'chunk' would have a greater speed, but the momentum of each chunk would be the same according to the conservation of momentum.
Problems:
6. 135 meters or 9 times further!
12. You'll have to click here for the answer