The Physics of
Impacts - Putting Momentum and Energy Together |
Purpose
In this lab investigation our purpose
is to investigate the role that momentum and energy play in any impact. Our
intention will be to formulate a general principle that we can apply to any*
collision process.
(*at least for collisions involving
velocities much less than the speed of light)
Key Terms
- perfectly elastic
collision: a
collision in which no kinetic energy is lost
- completely inelastic
collision: a collision in which the maximum amount of kinetic energy is lost.
- coefficient of
restitution 'e' is defined as the negative of the ratio of relative velocities before
and
after a collision. We can express this as
This is a very convenient parameter
to describe the elasticity
of a collision.
Pre-Lab Questions
- A 100 g mass (Puck A) is moving to the left with a speed of 2 m/s while a 200 g mass (Puck B) is moving to the right with a speed of 4 m/s. Express these as vectors and determine the relative velocity of Puck B with respect to Puck A.
- A 100 g mass with velocity [4 m/s,1m/s] collides and sticks to a 100 g mass moving with velocity [-2,-1] m/s. What is the magnitude of the momentum for each puck?.
- What is the momentum of the center
of mass (CM) for this system?
- What is the kinetic energy of
the CM? (Use Ek = p2/2m to calculate this)
- What is the kinetic energy of
each piece before the collision?
- How much energy was lost in this
collision? Where did this energy go?
- If the net momentum in the system is non zero is it possible to lose all of the kinetic energy in a collision?
- Formulate a general principle
that connects the kinetic energy and momentum of the parts of a system and
the CM of the system both before and after the collision.
Procedure
Review your data from the previous
lab (Momentum and the Center of Mass). You studied two cases - choose only the case in which the collision took place in an isolated frame to investigate the following 3 points:
- determine the relative velocities of the pucks before and after the collision. You will need to think how you can do this with the data you collected last week.
- determine the coefficient of restitution
for the collision. (You will need to explain carefully what you did here and
why)
- determine the kinetic energy of
the system before and after the collision and show how this supports the "general
principle" that you formulated in part 7 of the pre-lab.
What to Hand in
- On a separate sheet, each person in the group should
hand in his/her own answers to the pre-lab questions. This will be used to tabulate part of each individual lab grade.
- Each group should hand in a report in which you:
- present the data collected in the previous week and discuss how the CM behaves during a collision in an isolated system.
- present (in a logically arranged
table) the information you used to do parts 1,2 3 of the Procedure section
- prepare a statement or principle
that explains the role of the kinetic energy of the CM in any collision
in an inertial frame
- discuss the following statement:
True or False - in any collision in which momentum
is conserved , kinetic energy must also be conserved.
NOTE: For parts 2-4 you may
include worked numerical examples to help explain the general principle that
you develop.
.Use a standard report format in which you include a cover page, introduction, observations analysis and conclusions.
Date Due: Next Week