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Old 01-12-2003, 07:27 PM   #1
1st Gear Newbie
Join Date: Dec 2002
Location: Ohio
Posts: 11
Question Physics Problem...please help!

Attached is the physics problem from a former AP test. I don't even understand the question. Can someone help me understand/do the problem/tell me what year this test is from (if you ran into this problem years ago), etc. TIA!

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Old 01-12-2003, 08:49 PM   #2
Dave 325i
4th Gear Member
Join Date: May 2002
Location: .
Posts: 888
Well, that's a funny first post, but I'll see what I can do.

Draw a free body diagram. Gravity exerts a force down at the centre of mass of the rod, which is in the middle because the rod is uniform.

The pivot point exerts a force up, and the thread exerts a force up.

tau = I * alpha

tau is torque in Nm
I is the rod's moment of inertia in kg*m
alpha is angular acceleration in rad/sec*sec (sec squared)

You're given I in the question. You're looking for alpha. Torque is also given by: tau = rFsin(theta) Since the angle is 90 degrees sin(theta) is 1 and can be ignored.

So you're left with tau = rF. r is the distance from the pivot that force F is applied.

so you have

(l/2)*mg = I * alpha.

Not too sure about this one. Translational acceleration means in a straight line, like drag racers.

If I were desperate I'd just use F = ma but that seems too easy.

I think it's like (a) except the force from the string is no longer there.

Hardest part.
Go find your physics textbook and look up "Rotational Motion" It should have something like omega = omega(zero)*t + 0.5*alpha(zero)*t^2.

I believe that's where they key lies.

So, what mods on your car do you have? Surely you didn't join a BMW forum to ask a physics problem.

1987 BMW 325i
1A Offstream Mechanical Engineering / University of Waterloo
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Old 01-12-2003, 08:50 PM   #3
1st Gear Newbie
Join Date: Dec 2002
Location: Ohio
Posts: 11
Hey. Sorry this had to be my first post. I got a 93 325i and a 95 Acura Legend (winter car). I'm a senior in high school. Thanks for the excellent help!

The 325i has HID and 17's, the Legend is all stock.
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Old 01-12-2003, 10:16 PM   #4
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Join Date: Aug 2002
Location: Hamilton Ontario
Posts: 1,692
physics sucks ass

im taking it over again, i fucekd it up too hard in this semster, hahah
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Old 01-12-2003, 10:19 PM   #5
Join Date: Dec 2002
Location: HK
Posts: 2,538
I wish i could help u, i screwed up physics in high school and now I'm doing business in univeristy good luck

Wrangler Sahara 2015
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