Midterm
Exam
1
Biomechanics
IPHY
4540
Spring
2009
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your
TA/lab
section
Molly
Kelly
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Question
1
1A.
Imagine
a
skier
on
a
ski
lift
with
her
legs
dangling.
Diagram
and
explain
how
the
ankle
is
a
musculoskeletal
lever
system.
Indicate
the
location
of
the
muscle
(M),
joint
(J),
load
(L),
and
what
is
being
amplified.
Name
the
primary
muscle.
1B.
The
loading
in
figure
1,
is
commonly
experienced
during
a
forward
fall
while
skiing
and
could
potentially
result
in
fracture
of
the
tibia.
Indicate
on
the
diagram
the
type
of
bending
stresses
and
their
location
on
the
tibia
(T
and
C).
Also
indicate
where
the
tibia
is
most
likely
to
break
and
on
which
side.
Explain
why.
Assume
the
skier
is
a
young
adult.
Isometric
contraction
of
which
muscle
would
reduce
the
bending
stresses
on
the
tibia?
1C.
Children
often
experience
green‐stick
fractures,
where
the
bone
bends
before
it
breaks.
What
is
the
technical
term
used
to
describe
this
property?
What
differences
in
the
material
composition
of
bone,
compared
to
a
young
adult,
are
most
likely
responsible?
Use
stress­strain
curves
to
explain.
Would
you
be
more
confident
of
the
location
of
the
fracture
in
part
1B
if
the
skier
was
a
child?
1D.
In
the
diagram
below
is
a
representation
of
cortical
bone
remodeling
with
age
in
men
in
the
femoral
middiaphysis.
Between
ages
25
and
85,
ro
changes
from
1.5
cm
to
1.75
cm,
and
ri
from
0.75cm
to
1.0cm.
Calculate
the
change
in
cross­sectional
area.
Use
equations
to
show:
i)
why
this
change
is
beneficial
ii)
what
other
age­related
changes
may
cancel
out
these
benefits
Question
2
2A.
Imagine
you
have
10
sarcomeres;
each
generates
a
maximum
of
1
unit
of
force,
and
shortens
with
a
maximum
velocity
of
1
unit/s.
Diagram
an
arrangement
of
sarcomeres
that
will
create
a
muscle
fiber
with
the
following
force
and
velocity
characteristics.
Use
I
to
represent
individual
sarcomeres,
and
draw
ellipses
around
sarcomeres
to
specify
fibers.
i)
Fmax=
5
units;
Vmax=
2
units/s
ii)
Fmax=
2
units;
Vmax=5
units/s
iii)
Fmax=5cos10o
units;
Vmax=2cos10o
units/s
iv)
Fmax=5sin10
o
units;
Vmax=2sin10
o
units/s
2B.
Which
of
the
muscles
above
(i,ii,iii,iv)
would
you
be
least
likely
to
see
in
the
human
body?
Explain
why.
2C.
On
a
single
graph,
draw
the
force­velocity
curves
for
the
four
muscles
above
in
absolute
units.
Be
sure
to
label
the
axes
appropriately
(with
units).
Only
draw
the
shortening
velocity
half
of
the
graph
(positive
velocity)
2D.
On
a
single
graph,
draw
the
force­velocity
curves
for
the
four
muscles
above
in
normalized
units.
Be
sure
to
label
the
axes
appropriately
(with
units).
Only
draw
the
shortening
velocity
half
of
the
graph
(positive
velocity)
Question
3
3A.
Give
three
examples
(including
graphs)
of
viscoelastic
properties
of
tendon.
Be
sure
to
explain
the
examples
in
terms
of
the
conditions
under
which
the
data
were
obtained.
3B.
Oscar
Pistorius,
a
double
below‐knee
amputee,
was
initially
not
allowed
to
run
in
the
able‐bodied
2008
Olympics
because
it
was
determined
that
his
prosthetic
running
limbs
gave
him
an
advantage
over
able
bodied
runners.
Below
is
a
loading‐unloading
curve
for
the
Achilles
tendon
in
a
healthy
athlete,
and
a
hypothetical
loading‐unloading
curve
for
Pistorius’
prosthetic
limb.
Using
technical
terms,
describe
one
property
that
has
the
same
value
in
both
curves,
and
one
property
that
has
different
values.
Based
on
these
two
curves
alone,
explain
why
Pistorius
may
or
may
not
have
an
advantage.
Question
4
4A.
A
quarterback
releases
a
football
with
a
linear
velocity
of
30
m/s.
How
far
will
it
go,
if
he
releases
it
at
a
height
of
2.0m
and
with
a
10o
release
angle
(with
respect
to
horizontal)?
4B.
Name
three
factors
the
quarterback
can
change
to
increase
the
horizontal
distance
covered
by
the
pass.
Pick
one,
increment
it
by
10%,
and
use
calculations
to
prove
its
effect
on
horizontal
distance.
4C.
If
a
wide‐receiver
wanted
to
catch
the
ball
in
the
endzone
40
yards
(37
meters)
away
from
the
quarterback,
how
high
do
his
hands
need
to
be
in
order
to
catch
the
ball?
(Use
the
conditions
specified
in
part
4A)
4D.
The
wide‐receiver
is
10
yards
(9
m)
away
from
the
endzone
when
the
quarterback
throws
the
ball.
If
he
starts
running
the
instant
the
quarterback
releases
the
ball,
what
does
his
average
running
speed
need
to
be
in
order
to
catch
the
ball
in
the
endzone
at
the
height
calculated
in
part
C?
4E.
Based
on
your
knowledge
of
locomotion
kinematics,
why
may
the
wide­receiver
still
miss
the
pass?