PHYS 101 Lecture Notes - Lecture 7: Toonie
15 May 2018
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Phys 101: Tutorial 7. Momentum and collisions
Instructions: Print and bring with you to your tutorial. Read it over, but do NOT work on until your
tutorial time. Bring a calculator. And for this one, bring some coins like toonies, loonies, quarters.
Which coin is heavier, the toonie or the loonie? Your task in this tutorial is to find out, by doing an
experiment.
Question 1: As a first step, study a collision between two identical coins, such as two loonies, two
quarters, or two dimes. One of them (coin B) will be at rest initially, and the other one (coin A) will hit it
head on with speed 𝑣𝐴 . Remember, for elastic collisions in 1-D : 𝑣⃗𝐴 – 𝑣⃗𝐵 = −(𝑣⃗𝐴′ – 𝑣⃗𝐵′)
a) Before doing the experiment, draw a diagram of what you think will happen. Draw both coins
before and after the collision. (Assume momentum is conserved and the collision is elastic. The
latter won’t be true, since there is some dissipation with sound.)
b) How do you think coin B will move (speed and direction) after the collision? Why?
c) How do you think coin A will move (speed and direction) after the collision? Why?
d) Now try the experiment with several pairs of like coins: Place one coin on the table, and flick the
other one towards it with your finger. Do several trials for each pair of coins and record your
findings. (If the desktop is too rough, use a sheet of paper.) Which type of coin works best? Why
do you think that is?
