What is the correct formula for finding tension in a pendulum bob on a string?

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Homework Help Overview

The discussion revolves around determining the tension in a pendulum bob on a string, specifically when the bob reaches the highest point of its motion after being released with an initial velocity. The problem involves concepts from mechanics and energy conservation.

Discussion Character

  • Exploratory, Assumption checking, Conceptual clarification

Approaches and Questions Raised

  • The original poster attempts to apply Newton's second law to calculate the tension but questions the correctness of their approach after receiving conflicting feedback. Other participants inquire about the angle of the pendulum at its highest point and discuss the implications of the initial push given to the bob.

Discussion Status

Participants are exploring different interpretations of the problem, particularly regarding the angle at the highest point and the application of energy conservation principles. Some guidance has been offered regarding the use of energy methods, but no consensus has been reached on the correct approach.

Contextual Notes

The problem involves a pendulum bob with specific mass and length, and there is a mention of an initial velocity and angle, which may affect the calculations. The original poster expresses confusion about the role of the string length in their calculations.

chxmilan
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A 2 kg pendulum bob on a string that is 3m long is released with a velocity of 1 m/s when the support string makes an angle of 30 degrees with the vertical. What is the tension at the highest point of its motion?

The Attempt at a Solution


Ok so using Newton's second Law, the equation should be Force of tension =mg cos θ. Adding the numbers in =2 kg (9.80 m/s)cos 30°=16.97 N. However its telling me its wrong and the answer should be 16.6 N. I'm confused as to where I've gone wrong. I realize that I skipped over length of the string but I was told that because we're dealing the the vertical component, its not needed.
 
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What angle does it make when it's at its highest point?
 
Wouldn't the angle still be 30° at the highest point?
 
chxmilan said:
Wouldn't the angle still be 30° at the highest point?
It would be if it were released from rest at that point, but it was given a push.
 
I would suggest you to use energy instead.
 
agostino981 said:
I would suggest you to use energy instead.
One would use energy conservation to find the highest point, if that's what you mean.
 

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