Ph1a 2004 Homework 1 Solution
Chefung Chan ([email protected]), Fall 2004
Each homework problem is worth 5 points. Please disregard the point values listed on the problem itself.
Use the points listed below instead.
QP1 (5 points)
(a) (0.5 point)
22
11
2
0
(
9.8)
0.64 second
su
t
a
t
t
t
=+
⇒−
−⇒
=
(b)
(1 point) Since the ball is a ‘’Super’’ ball which bounces perfectly elastically from the
floor, the system is symmetric and the answer here should be the same as the answer
in part (a). That is
t
= 0.64 second too. If you don’t believe, work through it once. =)
(c)
(1.5 points) This question seems to be complicated. In fact, if you think about it
carefully, this case is also an INERTIAL FRAME !! Therefore, the system here is
equivalent to one in (a) and (b) and the answer here is also
t
= 0.64 second. Right now,
let’s do it explicitly.
12
2
1
Let
and
are the vertical coordinates of the ball and the lift floor relative to the
second floor where =0 there
1
and
2
(Notice the '
' in
here means the ball is movi
yy
y
y
s
ut
at
y
ut
ut
y
=+ +
=
2
2
ng upwards due to its inertia)
1
( It is the same equation as you find in (a)! )
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