Lab#11 Work-Kinetic Energy Theorem Activity

EXPT 1: Work done by a Non-constant Spring Force

  We measure the work done when we stretch a spring through a measured distance. First we will collect data for force applied by a stretched spring vs distance the spring is stretched, and we will plot a graph of force vs distance.Then we will be able to calculate the work done by finding the area under this graph.

Set up
  Set up the ramp, cart, motion detector, force probe, and spring as shown in the diagram, use cart"stops" or something else to support the spring so that it can be horizontal and unstretched. Be sure that the motion detector sees the cart over the whole distance of interest-from the position where the spring is just unstretched to the position.

     we got k = 2.956 N/m, EPE =(1/2)kx^2

Integral: 0.1274 N*m, the work that spring did on cart. 

EXPT 2: Kinetic Energy And The Work-Kinetic Energy Principle

  1. Use the same set up as above.
  2. measure the mass of the cart = 0.571 kg.
  3. be sure that the motion detector sees the cart over the whole distance of interest-from the position where the spring is stretched about 1.0 m to the position where it is just about unstretched. 
  4. Make sure that the x-axis of your graph is "position". Zero the force probe withe the spring hanging loosely. Then pull the cart along the track so that the spring is stretched about 1.0 m from the unstretched position.
  5. Begin graphing, and release the cart, allowing the spring to pull it back at least to the unstretched position. 

    Note that the top graph displays the force applied by the spring on the cart vs. position. It is possible to find the work done by the spring force for the displacement of the cart between any two positions. This can be done by finding the area under the curve using the integration ruutine in the software. The kinetic energy of the cart can be found directly from the bottom graph for any position of the cart.

    The work done by the spring is -0.2799 N*m, and the kinetic energy is 0.057 N*m.

The work done by the spring is -0.3145 N*m, and the kinetic energy is 0.256 N*m

The work done by the spring is -0.1941 N*m, and the kinetic energy is 0.313 N*m

    Find the change in kinetic energy of the cart after it is released from the initial position (where the kinetic energy is zero) to several different final positions.

Conclusions:

    The work done on the cart by the spring is equal to its change in kinetic energy. In any position,

EXPT 3:Work-KE theorem

    On the laptop is a movie file entitled Work-KE  theorem cart and machine for Phys 1.mp4. in the video, the professor uses a machine to pullback on a large rubber band. The force being exerted on the rubber band is recorded by an analog force transducer onto a graph.

    The stretched rubber band is then attached to a cart of known mass. The cart, once released, passes though two photo gates a given distance apart. By knowing the distance and the time interval between the front of the cart passing through the first photogate and then the second photogate, caculat the final speed and thus the final kinetic energy of the cart.At a convenient place in the movie, stop the movie, make a careful sketch the force vs position graph, and determine the work done by the machine in stretching the rubber band in it.