Download Physics 144 (section 1) Homework 4

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Physics
144
(section
1)
Homework
4
Due
date:
Friday,
Nov
13,
2009,
12:00
AM
(noon)
Place:
3rd
floor,
CEB
Drop
Box
labeled
Phys
144
(1),
near
elevator
Note:
you
may
skip
units
during
the
middle
of
the
computations,
but
the
end
result
must
have
it
or
you
will
get
a
deduction.
Write
down
what
you
understand
even
if
you
can’t
fully
solve
the
problem
to
get
partial
credits.
Late
submission
(after
first
pick­up
by
TA)
will
result
in
an
automatic
15%
markdown.
Furthermore,
any
submission
beyond
noon,
Monday
will
not
be
picked
up
or
graded..
Problem
1
(20
pt)
A
0.14‐kg
baseball
moves
toward
home
plate
with
a
velocity

v i = (−36 m/s)xˆ .
After
striking
the
bat,
the
ball
moves
vertically
upward
with
a

velocity
v f = (18 m/s)yˆ .
(a) Find
the
direction
and
magnitude
of
the
impulse
delivered
to
the
ball
by
the
bat.
Assume
the
ball
and
bat
are
in
contact
for
1.5
ms.
(b) How
would
your
answer
to
part
(a)
change
if
the
mass
of
the
ball
were
€
doubled?
(c) How
would
your
answer
to
part
(a)
change
if
the
mass
of
the
bat
were
doubled
instead?
Problem
2
(15
pt)
An
object
initially
at
rest
breaks
into
two
pieces
as
the
result
of
an
explosion.
One
piece
has
twice
the
kinetic
energy
of
the
other
piece.
What
is
the
ratio
of
the
masses
of
the
two
pieces?
Which
piece
has
more
mass?
Problem
3
(15
pt)
A
0.44
kg
block
of
wood
hangs
from
the
ceiling
by
a
string,
and
a
0.072‐kg
wad
of
putty
is
thrown
straight
upward,
striking
the
bottom
of
the
block
with
a
speed
of
5.74
m/s.
The
wad
of
putty
sticks
to
the
block.
(a) Is
the
mechanical
energy
of
the
system
conserved?
(b) How
high
does
the
putty‐block
system
rise
above
the
original
position
of
the
block?
Problem
4
(14
pt)
A
0.1
kg
stone
rests
on
a
friction‐less,
horizontal
surface.
A
bullet
of
mass
6.00
g,
traveling
horizontally
at
350
m/s,
strikes
the
stone
and
rebounds
horizontally
at
right
angles
to
its
original
direction
with
a
speed
of
250
m/s.
(a)
Compute
the
magnitude
and
direction
of
the
velocity
of
the
stone
after
it
is
struck
(b)
Is
the
collision
perfectly
elastic
and
why?
Problem
5
(20
pt)
A
1200‐kg
station
wagon
is
moving
along
a
straight
highway
at
12
m/s.
Another
car,
with
mass
1800
kg
and
speed
of
20
m/s,
has
its
center
of
mass
40.0
m
ahead
of
the
center
of
mass
of
the
station
wagon.
(a) Find
the
position
of
the
center
of
mass
of
the
system
consisting
of
the
two
automobiles.
(b) Find
the
magnitude
of
the
total
momentum
of
the
system
from
the
given
data.
(c) Find
the
speed
of
he
center
of
mass
of
the
system.
(d) Find
the
total
momentum
of
the
system
using
the
speed
of
the
center
of
mass.
Compare
to
your
results
in
part
(b)
and
comment.
Problem
6
(16
pt)
A
turntable
with
a
diameter
of
0.75
m
is
rotating
about
a
fix
axis
with
an
initial
angular
velocity
of
0.25
rev/s
and
a
constant
angular
acceleration
of
0.9
rev/s2
.
(a) Compute
the
angular
of
the
turntable
after
0.2
s
(b) Through
how
many
revolutions
has
the
turntable
spun
in
this
time
interval?
(c) What
is
the
tangential
speed
of
a
point
on
the
rim
of
the
turntable
at
t=0.2
sec?
(d) What
is
the
magnitude
of
the
resultant
acceleration
of
a
point
on
the
rim
at
t=0.20
s?