Physics 163

Unit 4: Momentum and Collisions

Problem Set A

Overview:

Problem Set A targets your ability to use the momentum equation and the impulse-momentumchange theorem in order to analyze physical situations involving collisions and impulses. You will need to have a solid grasp of at least four skills or conceptual understandings to be successful on Problem Set A. These skills include:

1. Momentum Equation: An object which is moving has momentum. The amount of momentum possessed by the moving object is the product of mass and velocity.
p = m • v
2. Impulse-Momentum Change Equation: In a collision, a force acts upon an object for a given amount of time to change the object's velocity. The product of force and time is known as impulse. The product of mass and velocity change is known as momentum change. In a collision the impulse encountered by an object is equal to the momentum change it experiences.

It will be crucial to understand the above relationship in this problem set. In many of the problems, a piece of extraneous information is provided. Without an understanding of the above relationships, you will be tempted to force such information into your calculations. Physics is about conceptual ideas and relationships; and problem sets test your conceptual understanding of these relationships. If you treat this problem set as a mere exercise in the algebraic manipulation of physics equations, then you are likely to become frustrated quickly. As you proceed through this problem set, be concepts-minded. Do not strip physics of its conceptual meaning.

3. Using an Equation as a Guide to Thinking: An equation can be treated as an algebraic recipe for problem-solving. But it also can be treated as a statement which describes qualitatively how one variable depends upon another. Two quantities in an equation could be thought of as being either directly proportional or inversely proportional. Thinking and reasoning proportionally about quantities allows you to predict how an alteration in one variable would effect another variable. You will need to use your proportional reasoning skills in Problem 9 of this set.
4. Calculation of Velocity Change: You will need to be able to calculate the velocity change of an object, particularly for a rebound situation. Velocity is a vector and is distinguished from speed in that it has a direction associated with it. This direction is often expressed in mathematics as a + or - sign. In a collision, an object expreieinces a force which causes a velocity change. The velocity change is computed by subtracting the initial velocity value from the final velocity value. If an object is moving in one direction before a collision and rebound or somehow changes direction, then its velocity after the collision has the opposite direction as before. Mathematically, the before-collision velocity would be + and the after-collision velocity would be - in sign. Ignoring this principle will result in great difficulty when analyzing any collision involving the rebounding of an object.

The above principles and their application to collisions can be reviewed at The Physics Classroom.

View Sample Problem Set.

 Problem Description Audio Link 1 Routine use of the equation for momentum 2 Routine use of the equation for momentum 3 Routine use of the equation for momentum 4 Routine use of the equation for momentum 5 Routine use of the equation for impulse-momentum change equation 6 Use of the impulse-momentum change equation 7 Use of the impulse-momentum change equation in a problem involving inconvenient units 8 Routine use of the equation for momentum 9 Use of the impulse-momentum change equation as a guide to thinking qualitatively 10 Use of the impulse-momentum change equation in a physical situation involving direction change 11 Use of the impulse-momentum change equation in a rebounding situation 12 Use of the impulse-momentum change equation and the computation of the final velocity from velocity change 13 Use of the impulse-momentum change equation 14 Use of the impulse-momentum change equation

Audio Help for Problem: 1 || 2 || 3 || 4 || 5 || 6 || 7 || 8 || 9 || 10 || 11 || 12 || 13 || 14

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