4-page lab

Abstract: We want to test out the Work Kinetic Energy Theorem: Does the net work done on an object equal the object’s change in kinetic energy? Does W = KE?

Theory: Draw a sketch of a graph of force vs position assuming a constant force.

What does the area under the graph represent?

Draw another sketch of a graph of force vs position assuming a brief, non-constant force.

Even though the force is variable, what thing will still represent the Work?

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Work Kinetic Energy Lab

Procedure: I connected a force probe and motion detector to the LabQuest Mini. Sketch a side view of the set-up on this page: a horizontal track with a force probe mounted on a cart, with a string pulling horizontally to the right. A motion detector at the left end of the track records the carts speed. See photos…

A variable force F was applied to the right, on the cart of mass m over a displacement Δx. On your laptop with LoggerPro installed, do Alt click to download the Data file, then open it in LoggerPro.

Note that the LoggerPro graphs are: F vs x and v vs x. Time t is not on the horizontal axis.

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Data:

Find the work done on the cart by the pull force. Click and drag to select the entire pull on your graph of F vs x. Then click on the Integral button at the top of the screen: this will give you the area.

Do not find the area under your v vs x graph. What we need from this graph is the maximum cart speed.

Select the appropriate part of your v vs x graph and click on the Stats Button (hover over the buttons until you locate it) to find vmax.

Delete the data table and rescale your graphs (F vs x and v vs x) making sure the x-axis numbers line up. Click on Print (not Print Graph) making sure that you have both pop-up data boxes for your graphs. Tape graphs with their both pop-up data boxes onto of this page in your PJ.

Next, get the cart mass m from this picture:

3 m = kg

Your velocity should peak right after your force returns to 0.v

x

F

x

Note that the mass on the right side of the scale is 1.000 kg. You need to add that to the slider readings…

Calcs:

We call the quantity ½ mv2 the Kinetic Energy. Kinetic Energy KE = ½ mv2

Does the work (area) from your graph of F vs x equal the cart’s change in kinetic energy? Test it out!

Don’t forget the units!

Big Result:

Do a percent difference calculation:

Does Work = ΔKE? State your result!4

Work = ½ mvf2 - ½ mvo

2 =

% Difference = |value 1 – value 2| x 100 = average value