Conservation of Energy Question

In summary, the conversation is about a physics student seeking help with a question on calculating the efficiency of a pendulum. The student has been provided with information about the mass, diameter, initial height, length of string, and time interval of the pendulum, but is unsure if it is enough to determine the speed and efficiency. The expert suggests using the change in potential energy and interruption time to calculate the kinetic energy and efficiency, though it would be better to have multiple measurements. The student also has a question about the relevance of the bob diameter in determining velocity.
  • #1
homeslice
3
0
Hi, there. I'm doing a correspondance physics course, and this one question has me stumped. I'm calculating the efficiency of a pendulum, and therefore need to find the mechanical energy, as well as the thermal energy. However, I don't think they've given me enough information.

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 photogate light interruption = 11.8 ms

*The photogate light interruption happens at the lowest point of the pendulum swing.

Thanks for your help,
-Gary
 
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  • #2
You would certainly need to know the speed of the pendulum at various times- if the pendulum were 100% efficient (no friction) then you could find the speed as a function of time from the given information but to determine the efficiency, you will need to know how it slows down.
 
  • #3
Yeah, I know that. My problem is that I can't figure out how to get the speed, because I don't know the distance that the bob has travelled. Is it actually possible to determine the speed with the information that I have?
 
  • #4
homeslice said:
Yeah, I know that. My problem is that I can't figure out how to get the speed, because I don't know the distance that the bob has travelled. Is it actually possible to determine the speed with the information that I have?

It's not an ideal situation, but in principle you have been given enough information. You can calculate the change in potential energy of the pendulum based on starting height relative to the bottom and you can calculate the kinetic energy at the first pass through the lowest point of the swing by using the interruption time and bob diameter to find velocity. From this you can find the energy "lost" in the first quarter cycle of the motion, an calculate an efficiency.

It would be better if you could measure velocity for multiple passes, but you have to use what you are given.
 
  • #5
How does the diameter of the bob have anything at all to do with the velocity?
 
  • #6
homeslice said:
How does the diameter of the bob have anything at all to do with the velocity?
The bob is what interrupts the light beam. The beam is blocked for the time it takes the bob to move one diameter.
 

FAQ: Conservation of Energy Question

What is conservation of energy?

Conservation of energy is a fundamental law in physics that states that energy cannot be created or destroyed, it can only be transferred from one form to another.

Why is conservation of energy important?

Conservation of energy is important because it helps us understand and predict the behavior of physical systems. It also allows us to develop technologies that are more efficient and sustainable.

What are some examples of conservation of energy?

Some examples of conservation of energy include a pendulum swinging back and forth, a ball rolling down a hill, and a battery powering a light bulb.

How does the law of conservation of energy relate to the first law of thermodynamics?

The first law of thermodynamics is essentially a restatement of the law of conservation of energy in the context of thermodynamic systems. It states that the total energy of a closed system remains constant.

What happens when energy is not conserved?

If energy is not conserved, it means that it has been lost or gained through some process. This can lead to unexpected and unpredictable results in physical systems and can have negative impacts on the environment.

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