1. Module 2

1.14. Page 5

Lesson 2

Module 2—The Conservation of Momentum in Isolated Systems

Read

 

Read “Inelastic Collisions” on page 483 of your physics textbook. Continue by studying “Example 9.10” on pages 484 and 485 of your textbook.

 

Self-Check

 

SC 4. Answer “Practice Problem 1” on page 484 of your textbook.

 

Check your work.
Self-Check Answers

 

SC 4.

 

Given

 

 

     mp = 1.00 kg           

 

Required

 

The velocity of the bullet just before impact, .

 

Analysis and Solution

 

Choose the system of bullet and pendulum as an isolated system. Since the pendulum is stationary before the bullet hits, its initial velocity is zero; thus, its initial momentum . After the collision, the bullet and pendulum move together as a unit. The kinetic energy of the pendulum-bullet system is converted into gravitational potential energy:

 

Ek = Ep

 

Apply the law of conservation of energy to find the speed of the pendulum-bullet system just after impact:

 

 

Apply the law of conservation of momentum to find the initial velocity of the bullet:

 

 

Paraphrase

 

The initial velocity of the bullet immediately before impact was 391 m/s [forward].

 

Read

Study “Example 9.11” on page 485 of your textbook.

 

Self-Check

 

SC 5. Answer “Practice Problem 1” on page 485 of your textbook.

 

Check your work.
Self-Check Answers

 

SC 5.

 

Given

 

mass of dart md = 0.012 kg

 

mass of block-glider mb = 0.200 kg

 

final velocity of system

 

initial velocity of dart

 

Required

 

The amount of kinetic energy lost immediately after the interaction.

 

Analysis and Solution

 

the initial energy of the system comes from the kinetic energy of the dart:

 

 

The final kinetic energy comes from the dart-block-glider system.

 

 

The difference between the initial and final kinetic energies is the kinetic energy lost.

 

 

Paraphrase

 

There was 1.1 J lost immediately after the interaction of the dart and the block-glider system.

 

Try This

 

TR 1. Answer “Practice Problem 2” on page 484 of your textbook.

TR 2. Answer “Practice Problem 2” on page 485 of your textbook.

 

Module 2: Lesson 2 Assignment

 

Remember to submit the answers to A 3 to your teacher as part of your Module 2: Lesson 2 Assignment.

 

A 3. Design an experiment that would let you answer the following problem:

 

Is the collision between a ball pendulum and a block pendulum elastic, inelastic, or completely inelastic?

 

The following four diagrams give you a starting point for your experiment.

 

An image shows four positions for a clay pendulum and wooden block pendulum. Picture 1 shows the two hanging and touching at the bottom.

 

Picture 2 shows the clay pendulum pulled back and the wooden block hanging.

 

Picture 3 shows the clay pendulum swinging down and striking the wooden pendulum.

 

Picture 4 shows the clay ball and the wooden pendulum bouncing away from each other after colliding.

 

 

From “Examples 9.10” and “9.11” of your textbook, you will be familiar with using gravitational potential energy to find the kinetic energy of a ball pendulum. You can deal with the kinetic energy of the block pendulum in a similar fashion.

 

You need to present the following in your experimental design:

  • the measurements that need to be taken

  • the calculations that would have to be made

  • the criteria you would use to answer the problem