practice

1. Which would you rather be hit by: the fastest pitched baseball or the fastest served tennis ball? To answer this question determine the following quantities …
   1. the momentum of each ball
   2. the impulse delivered if the baseball stops dead on impact but the tennisball rebounds at nearly the same speed.
   Write your answers in the table below.
   
   

   quantity	baseball	tennisball
   mass	145 g	57 g
   speed	45 m/s	75 m/s
   momentum
   impulse

   
   
2. Analyze This:

   Now, the bears I live with average, the males, eight to twelve hundred pounds [360-540 kg]. They're the largest bears in the world …. They've been clocked at 41 [mph] and they've run a hundred meter dash in 5.85 seconds, which a human on steroids doesn't even approach.
   Timothy Treadwell author of Among Grizzlies. The Late Show with David Letterman. NBC. 20 February 2001.

3. Analyze This:

   about one atom per cubic centimeter … At two-tenths the speed of light, dust and atoms might not do significant damage even in a voyage of 40 years, but the faster you go, the worse it is -- space begins to become abrasive. When you begin to approach the speed of light, hydrogen atoms become cosmic-ray particles, and they will fry the crew …. So 60,000 kilometers per second may be the practical speed limit for space travel.
   Isaac Asimov. "Sail On! Sail On!" The Relativity of Wrong. New York: Kensington, 1996: 220.

4. Write something completely different.

conceptual

1. In older passenger cars, body panels were attached to a single frame around the perimeter, making them very rigid. This is known as body-over-frame construction. In newer cars, different body parts have stress-bearing elements within them and these parts are then welded to each other. This is known as unitized body construction. Repairing "unibody" cars after collision is comparatively difficult as stress (and thus damage) are distributed throughout the different parts. Why then are cars now built this way?
2. To escape from a horrible fire, two people are forced to jump from the third story of a burning building on to solid concrete. Which person is more likely to sustain serious injuries: the jumper who comes to an abrupt halt when he lands or the jumper who bounces after impact?

numerical

1. When hit, the velocity of a 0.145 kg baseball changes from +20 m/s to −20 m/s. What is the magnitude of the impulse delivered by the bat to the ball?
2. A rubber ball of mass 0.025 kg traveling at 4.0 m/s down strikes the floor and bounces straight up at 2.0 m/s. Find the magnitude of the impulse that the floor gave to the ball.

investigative

1. Plate
   Antarctic
   African
   Arabian
   Caribbean
   Cocos
   Eurasian
   Indian
   Nazca
   North American
   Pacific
   Philippine
   South American

   Determine the momentum of one of earth's tectonic plates (sometimes referred to as continental plates). A list of the most popular plates is shown on the right.
   1. Answer these three related questions first.
      1. Which plate have you chosen to work with?
      2. What is the speed of this plate?
      3. What is the area of this plate?
   2. Now answer these three related questions.
      1. Is the plate you've chosen continental or oceanic?
      2. What is a typical density of this kind of crust?
      3. What is a typical thickness of this type of crust?
   3. Compute the momentum of the tectonic plate you've chosen from the data you've found. State your answer to the nearest order of magnitude (the nearest power of ten). Don't forget the unit.