Part
(c)
Suppose
instead
he
keeps
his
arms
in
and
allows
friction
of
the
ice
to
slow
him
to
75
rev/s.
What
is
the
magnitude
of
the
average
torque
that
was
exerted,
in
N
-
m,
if
this
takes
17
s?
Let's
begin
by
stating
the
relationship
between
the
torque,
moment
of
inertia,
and
angular
acceleration.
T
Ia
Next,
let's
use
rotational
kinematics
to
write
an
expression
for
the
angular
acceleration
in
terms
of
the
angular
velocity
and
time.
wy
w
|
at
Now
that
we
have
an
expression
for
the
angular
acceleration,
but
note
that
it
will
only
apply
if
the
values
we
have
for
angular
velocity
are
in
radians
per
second.
As
such,
we
need
to
convert
both
of
the
angular
velocities
before
we
continue.
Let's
begin
with
the
initial
angular
velocity.
52rev
2xrad
1s
1
rev
w
w
—
(5.2-2x)
rad/s
Let's
repeat
this
process
for
the
final
angular
velocity.
25rev
2rxrrad
“s
1s
1
rev
w3
(2.5
-
2!’)
md/s
We
can
now
use
the
relationship
between
torque,
moment
of inertia,
and
angular
acceleration
to
find
the
average
torque.
Tave
Ia
Tave
ICI
I
2
(2.5-2x)
rad/s
—
(5.2-2x)
rad/s
Tave
—
0.24kg
-m
1is
Taee
—
0.3701
rad
/s
