Posted by Anonymous on Sunday, December 8, 2013 at 4:29pm.
A ruler stands vertically against a wall. It is given a tiny impulse at θ=0∘ such that it starts falling down under the influence of gravity. You can consider that the initial angular velocity is very small so that ω(θ=0∘)=0. The ruler has mass m= 200 g and length l= 20 cm. Use g=10 m/s2 for the gravitational acceleration, and the ruler has a uniform mass distribution. Note that there is no friction whatsoever in this problem. (See figure)
(a) What is the angular speed of the ruler ω when it is at an angle θ=30∘? (in radians/sec)
ω=
(b) What is the force exerted by the wall on the ruler when it is at an angle θ=30∘? Express your answer as the x component Fx and the y component Fy (in Newton)
Fx=
Fy=
(c) At what angle θ0 will the falling ruler lose contact with the wall? (0≤θ0≤90∘; in degrees) [hint: the ruler loses contact with the wall when the force exerted by the wall on the ruler vanishes.]
θ0=

PHYSICS(ELENA  fima, Sunday, December 8, 2013 at 7:00pm
apply conservation of energy:
U=m*g*hcm
EK= 1/2*I*w^2, I=1/3*m*L^2
Eini= mg(L/2) + 0
Efin= mg(L/2)cos30 + 1/2*I*w^2
solve for Eini=Efin > w=
any one knows how to aswer the other questions?

PHYSICS(ELENA  C_P, Monday, December 9, 2013 at 12:39am
did this work for you? are you sure that we shouldn't use parallel axis theorem to find I? Because rod is rotating about end. And you assume that it's a point mass in the rotational motion.

PHYSICS(ELENA  an0nym801, Monday, December 9, 2013 at 3:04am
I don't think so.
omega comes out too low
I think part a) has to be done with energy conservation
U at the top  U at 30° = K of rod

PHYSICS(ELENA  fima, Monday, December 9, 2013 at 9:23am
the equation is Ok, and the w value got green checked. So YES, I'm sure about A.
And I did for conservation of energy.
But anyone knows how to do B and C. And please, try to post the procedure, because we all have different data.

PHYSICS(ELENA  koala, Monday, December 9, 2013 at 10:03am
Can you guys help me with questions 2 and 3 ? I just have one more try but i am really confused in this two ;(
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