Lecture 4 Notes (PDF) - SFSU Physics & Astronomy

Example: The Flying Cap
Upon graduation, a joyful student
throws her cap straight up in the air
with an initial speed of 14.7 m/s.
(Neglect air resistance.)
What is acceleration of cap?
(a) When does cap reach its highest
point?
(b) What is the distance to the
highest point?
(c) Assuming the cap is caught at
same height it was released, what is
total time cap was in flight?
1. Draw the cap (as a dot) in its
various positions.
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2. (a) Use the time, velocity and acceleration relation.
vx
− v0
x
(0 m/s) − (14.7 m/s)
vx = v0 x
+ ax∆t; ∆ t = = = 1.5 s
2
a −9.81
m/s
x
(b) Use average velocity: v av = v 0 /2 = 7.35 m/s;
∆x = v av ∆t=(7.35 m/s)(1.5 s) = 11.0 m
(c) Up time = down time, so total time is 3.0 s. (see text
for a more complicated method.)
3. The answers have the right units and seem reasonable.
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