Mechanical energy in a pendulum

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SUMMARY

The forum discussion focuses on calculating the mechanical energy of a pendulum and verifying the law of conservation of energy. Key measurements include a pendulum bob mass of 240.3 g, a diameter of 3.50 cm, an initial height of 48.0 cm, and a string length of 2.14 m. The calculated mechanical energy at the starting position is 1130.37 J, and the speed of the pendulum bob at the lowest point is approximately 2.97 m/s. The discussion emphasizes the importance of using correct units in energy calculations to ensure accurate results.

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Shaley
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A pendulum was set up and measurements were made to enable the mechanical energy to be calculated at the start position S and the lowest point of the pendulums swing L.

The mass of the pendulum bob was determined on an electronic scale and its diamter was measured using calipers. The initial height was measured with a meter stick. At the lowest point of its swing, the pendulum bob broke a photogate light beam. The time interval that the light was interrupted was recorded on an electronic timer attached to the photogate.
Use the following data to complete a report.
MAss of pendulum bob = 240.3 g
Diameter of pendulum bob = 3.50 cm
Initial height of pendulum bob = 48.0 cm
Length of pendulum string = 2.14 m
Time interval of photogate light interruption = 11.8 ms

Your report should include the following:
(a) conclusion as to whether or not the pendulum demonstrated the law of conservation of energy
(b) calculations of the efficiency of the pendulum as a mechanical machine

I am really confused how to even start this question. I think that I should figure out the Emechanical = Ek + eg

=1/2(240.3)(0) + 240.3(9.8)(.48)
=1130.37J

to calculate the speed of when it hit, I did the following:

The clue is the diameter of the bob
it broke the beam for 11.8 *10^-3 seconds
it is .035 meters in diameter
so it went
.035 meters in 11.8^10^-3 seconds
which is about 2.97 meters/s

From here, I don't really know where to go. Please help me.
 
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Shaley said:
I am really confused how to even start this question. I think that I should figure out the Emechanical = Ek + eg

=1/2(240.3)(0) + 240.3(9.8)(.48)
=1130.37J
You have made a good start. There is an issue with the units here; to get energy in Joules, you must use m, kg, and s for the other units. One of quantities in your Eg calculation is in the wrong units.

to calculate the speed of when it hit, I did the following:

The clue is the diameter of the bob
it broke the beam for 11.8 *10^-3 seconds
it is .035 meters in diameter
so it went
.035 meters in 11.8^10^-3 seconds
which is about 2.97 meters/s

From here, I don't really know where to go. Please help me.
You can now do the calculation of Etotal=Ek+Eg for when the pendulum is at the bottom of its swing.
 

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