Michael Bowles
Test 1  Solutions
Dr. Ballmer
PHY 101
Problem 1.1
If an object, such as arrow, is projected vertically the only thing that will change the motion
will be gravity, because we have decided to neglect fristion/air resistance. We know from the
top of the page that gravity has a constant magnitude of 9
.
8
m
s
2
. We also know that
v
f
(
t
) =
v
0
+
a
·
t
Given that acceleration is constant and negative we have an equation of the form
y
(
x
) =
m
·
x
+
b
We know that the arrow was projected upward (so there’s a positive initial velocity correspond
ing to the
b
 the yintercept).
So we have a downwardsloping straight line with an initial value above the
x
axis.
Problem 1.2
If we drive around a curve, and suddenly friction fails (as an example) we we continue in the
direction we are currently traveling. For uniform circular motion the velocity is always pointing
forward as in the image below.
Figure 1: An object pulled along a circular path (taken from Wikipedia)
We know from Newton’s first law that an object in motion, stays in motion (Unless acted upon by
an external force). So whatever the direction of our velocity before friction fails is where we go af
terwards as well.
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 Fall '08
 Schwarz
 Resistance, Force, Friction, Gravity, Mass, Michael Bowles, Dr. Ballmer

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