PHYS Review Questions CH 6

18. Distinguish between an elastic collision and an inelastic collision. For which type of collision is momentum conserved

In an elastic collision there is no generation of heat or deformation, while in an inelastic collision there is. Momentum is conserved for inelastic collisions.

1. Which has greater momentum, a heavy truck at rest or a moving skateboard

The moving skateboard because the heavy truck at rest has no momentum because it has no speed.

16. What does it mean to say that momentum (or any quantity) is conserved

When it is said the momentum is conserved that means there is no change.

22. In the preceding question, what is the total momentum of the balls of putty before and after the collision

√2

13. In the preceding question, in which case is the greatest impulse required

A baseball that is caught and then thrown back

20. If the equally massive cars of the previous question stick together after colliding inelastically, how does their speed after the collision compare with the initial speed of car A

After the collision the speed is half as much as the velocity of the initial speed of Car A.

11. In boxing, why is it advantageous to roll with the punch

Because it extends the time and diminishes the amount of force that will be received.

21. Suppose a ball of putty moving horizontally with 1kg*m/s of momentum collides and sticks to an identical ball of putty moving vertically with 1kg*m/s of momentum. Why is their momentum not simply the arithmetic sum of 2kg*m/s

Because just as the diagonal of a square is not simply the sum of two sides, the same way the momentum of the two balls cannot be the simple addition of both momentums.

10. In Karate, why is a force that is applied for a short time more advantageous

Because since the time of contact if very short, the force applied to the object is greater.

8. Why is it a good idea to have your hand extended forward when you are getting ready to catch a fast-moving baseball with your bare hand

Because that way you have room to let your hand move backward after contact is made with the ball. This extends the time of impact and reduces the force of impact.

4. For the same force, why does a long canon impart more speed to cannonball than a small canon

Because the long canon has a greater impulse because of the period of time the force is applied.

9. Why would it be a poor idea to have the back of your hand up against the outfield wall when you catch a long fly ball

Because then there is no space for your hand to move backward and the force of impact will be greater.

6. To impart the greats momentum to an object, should you exert the largest force possible, extend that force for as long a time as possible, or both

Both

14. Can you produce a net impulse on an automobile by sitting inside and pushing on the dashboard

Can the internal forces within a soccer ball produce an impulse on the soccer ball that will change its momentum?No, because internal forces will not produce a change in momentum.

19. Railroad car A rolls at a certain speed and makes a perfectly elastic collision with car B of the same mass. After the collision, car A is observed to be at rest. How does the speed of car B compare with the initial speed of car A

Car B was at rest when Car A rolled at a certain speed and made an elastic collision with car B.

2. How does impulse differ from force

Impulse has to do with time, it is the amount of force sustained for a period of time.

17. When a canon ball is fired, momentum is conserved for the system of a canon plus cannonball. Would momentum be conserved for the system if momentum were not a vector quantity

No, because then they would not be able to cancel.

15. Is it correct to say that, if no net impulse is exerted in a system, then no change in the momentum of the system will occur

Yes, because if there is no external impulse exerted in a system then there will be no change in momentum.

5. Is the impulse-momentum relationship related to Newton's second law

Yes, the impulse-momentum relationship is derived by rearranging Newton's second law to make the time factor more evident.

7. When you are in the way of a moving object and an impact force is your fate, are you better off decreasing its momentum over a short time or over a long time

You are better off decreasing its momentum over a long period of time because it reduces the force and decreases the resulting acceleration.

3. What are the two ways to increase impulse

You can increase the impulse by increasing the force applied or by increasing the period of time the force is applied.

12. Which undergoes the greatest change in momentum: a. A baseball that is caught b. A baseball that is thrown c. A baseball that is caught and then thrown back If all of the baseballs have the same speed just before being caught and just after being thrown

c. A baseball that is caught and then thrown back