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Work and Kinetic Energy with Interactive Physics

Copy the file W110WorkKE.IP (from the server Team Physics 311/Interactive Physics folder) onto your MyDocuments. The file uses software called Interactive Physics which simulates the physical world.

A 5.0 kg box is shown on a horizontal frictionless surface. When you depress a button, a 10 N force is applied to the right.

Useful controls: Run, Stop, Pause on the top toolbar.

Along the bottom of window controls for rerunning the simulation, especialy the "| >" and "< |" buttons.

To begin the simulation, click the Run button.

To apply a constant 10.0 N force in the +x-direction, click and hold the "Force 3" On/Off button.

To erase previous data, stop and reset the simulation, and click the "Force 3" button.

Graphs of velocity versus time and force versus position are shown, as well as readouts of time, position, and velocity.

1. Click run and begin applying a force at t=2 seconds. Apply the constant force until the box's velocity is v=4 m/s.

For how many seconds was the force applied?
How far did the box travel in this time?
What is the Kinetic Energy of the box?

2a. Now you want to triple the final velocity.

By what facor will the time change? Same time, Square Root(3) larger, 3x larger, 9x larger, other
By what factor will the distance change? Same time, Square Root(3) larger, 3x larger, 9x larger, other
By what factor will the Kinetic Energy change? Same KE, Square Root(3) larger, 3x larger, 9x larger, other

2b. Now test your prediction from 2a. Begin applying the force at t=2 seconds.

By what factor did the time change?
By what factor did the distance change?
By what factor did the Kinetic Energy change?

3. Instead you want to triple the distance that the box travels.

By what facor will the time change? Same time, Square Root(3) larger, 3x larger, 9x larger, other
By what factor will the speed change? Same time, Square Root(3) larger, 3x larger, 9x larger, other
By what factor will the Kinetic Energy change? Same KE, Square Root(3) larger, 3x larger, 9x larger, other

3b. Now test your prediction.

By what factor did the time change?
By what factor did the speed change?
By what factor did the Kinetic Energy change?

If you have time, do the following

Work-Kinetic Energy for a Variable Force

Time permitting

Copy the Interactive Physics file W110VariableForce.IP to MyDocuments. This shows a ball starting from rest at a location x = 1.0 m and acted on by a force F = 9.0/x2 N m2 . Use the work-kinetic energy theorem (Kinitial + Wnet = Kfinal ) to predict the speed when x = 4.0 m. Run the simulation and see if your prediction is correct.

[Hint: We have described the work as the area between the curve and the x-axis on a plot of force versus position. How do you use calculus to determine area?]