Understanding the Dynamics of a Simple Pendulum

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A simple pendulum consists of a mass M suspended by a string, swinging between angles +,- theta0. The tension T in the string varies with the angle of the pendulum. It is largest at the lowest point (theta=0) and smallest at the maximum angles (+,- theta0). The vertical component of tension remains constant, while T does depend on theta. The confusion arises from the misconception that T equals Mg at certain angles, which is incorrect when the mass is in motion.
vroman
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A simple pendulum consists of a mas M suspended by a thin string. The magnitude of the tension is T. The mass swings back and forth between +,- theta0.
I need help identifying which of the following statements are correct. These are my answers, but I'm getting something wrong.

A)T=Mg at some angle between zero and theta0 not correct
B)T is largest at the bottom (theta=0)
Correct
C)The vertical component of tension is constant Correct
D)T is smallest when theta=+,- theta0
Correct
E)T depends on theta Correct
F)T equals Mg when theta=theta0
Not correct
G)T is greater than Mg for theta =theta0 Not correct

I would really appreciate some help with this problem, Thanks!
 
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Discuss "A".Why do you think it is incorrect...?

Daniel.
 
Because I thought T=mg at 0.
 
vroman said:
Because I thought T=mg at 0.

Only if the mass is not accelerating at 0, and the only time that happens is if the mass is at rest at zero. Your mass is always moving at 0. What is the direction of acceleration at that point?
 
The book claims the answer is that all the magnitudes are the same because "the gravitational force on the penguin is the same". I'm having trouble understanding this. I thought the buoyant force was equal to the weight of the fluid displaced. Weight depends on mass which depends on density. Therefore, due to the differing densities the buoyant force will be different in each case? Is this incorrect?

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