Pendulum - Kinetic Energy at Lowest Point?

  • Thread starter crazyog
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  • #1
crazyog
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[SOLVED] Pendulum - Kinetic Energy at Lowest Point?

1. The Problem Statement:

A pendulum of length L= 1.0 m with an attached bob of mass m= 0.2 kg is released from a point where the cord makes an angle of 30 degrees with the vertical. The kinetic energy of the bob at its lowest point is...?
a. 2.0 J,
b. 1.7 J,
3. 1.1 J,
4. 1.0 J,
5. 0.26 J


Homework Equations


I believe Relevant equations include:
(1/2)mv^2 -- kinetic energy
(mgy) -- potential energy


The Attempt at a Solution


I know that at the lowest point in the pendulum, it is the highest speed. There is no potential energy. But, how do I get the value for velocity?
 
Last edited:

Answers and Replies

  • #2
nicksauce
Science Advisor
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Well from conservation of energy, the maximum potential energy is equal to the maximum kinetic energy. Can you calculate the maximum potential energy?
 
  • #3
crazyog
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Ok so Maximum potential energy would be where it is released...
Thus,
U= gmy
(9.8)(0.2)(y)
and (y) is the height it is released so when I solve for that
and I get (1-cos(30)
U=gmy
(0.2)(9.8)(1-cos(30))
=0.26

and I just realized that my professor said the answer was E.
Thank you!!!!!
 

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