Work and Kinetic Energy

  • #1

Homework Statement


This is a lab I did for physics. In this experiment, a glider starting from rest on an air track is attached to a string. The string is drawn over a pulley with a mass hanger tied to the other end. Work is done by gravity which results in a gain of kinetic energy of the entire system. There is a motion sensor located at the left end of the air track, which is where I got the data on the left side of the picture. I placed my hand on the glider, turn on the fan, wait for 3.4 seconds before letting go of the glider and the glider moves to the right. The glider hits the end of the air track and that's the end of data collection. There is a question in the picture which is question #14.

#14.) The total system (glider + hanger + masses) is moving with a velocity given by the velocity data you exported. Calculate the change in kinetic energy of the system relative to the initial kinetic energy (zero kinetic energy relative to the motion sensor when starting from rest) at each time the velocity was taken. This should be done in excel to be used for a graph requested later.

Below this question in the picture is my attempt.

My question: What will be my new and final data points after the calculations that I showed? Of course, I will not be doing this by hand, I will be doing it on excel, but I’m just showing the calculations for the purpose of showing how I am thinking. In the question, it says, “Calculate the change in kinetic energy of the system relative to the initial kinetic energy (zero kinetic energy relative to the motion sensor when starting from rest) AT EACH TIME THE VELOCITY WAS TAKEN”.

My first set of calculation had initial velocity = 0.07m/s and final velocity = 0.03m/s. Does that mean that my next calculation will use initial velocity = 0.03m/s and final velocity = 0.12m/s?

I’m really confused. Below is a link to all the information, data collected and illustration of the lab setup that you need to know. If you need any more information, please ask. Thanks!

Use this link, it's clearer. Just zoom into see better.
https://myhpu-my.sharepoint.com/per...cedc60b090147&authkey=ASjBnzRP8Gxa2cRQW2GTupo

Homework Equations


It's all in part 1

The Attempt at a Solution


It's all in part 1
 

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Answers and Replies

  • #2
haruspex
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My first set of calculation had initial velocity = 0.07m/s and final velocity = 0.03m/s.
That clearly makes no sense. There is a risk that the initial movement is confused by the way you let go of the glider. It might jitter a little. I would start at the last value that shows a position of .47.
 
  • #3
kuruman
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Does that mean that my next calculation will use initial velocity = 0.03m/s and final velocity = 0.12m/s?
I think it means constructing a column with entries ΔKi = Ki - 0, in other words the instantaneous kinetic energy assuming that you start at zero. That is how I interpret the statement between parentheses in “Calculate the change in kinetic energy of the system relative to the initial kinetic energy (zero kinetic energy relative to the motion sensor when starting from rest) AT EACH TIME THE VELOCITY WAS TAKEN”. I don't think you are asked to find changes in kinetic energy between adjacent velocity readings, i.e. ΔKi = Ki+1 - Ki. However, I agree with @haruspex that the first two readings need explaining. What is the accuracy of your measurements?
 
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  • #4
I think it means constructing a column with entries ΔKi = Ki - 0, in other words the instantaneous kinetic energy assuming that you start at zero. That is how I interpret the statement between parentheses in “Calculate the change in kinetic energy of the system relative to the initial kinetic energy (zero kinetic energy relative to the motion sensor when starting from rest) AT EACH TIME THE VELOCITY WAS TAKEN”. I don't think you are asked to find changes in kinetic energy between adjacent velocity readings, i.e. ΔKi = Ki+1 - Ki. However, I agree with @haruspex that the first two readings need explaining. What is the accuracy of your measurements?

That clearly makes no sense. There is a risk that the initial movement is confused by the way you let go of the glider. It might jitter a little. I would start at the last value that shows a position of .47.
Alright, I'll try that.
 

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