Experiment 6: Work & Energy
EXPERIMENT 6: WORK AND ENERGY
Objective:
To validate the work-energy theorem and to study the conservation of energy principle.
Theory:
The work-energy theorem states that the net (total) work done on a system is equal to its increase
in kinetic energy. You will determine the work done on a (nearly) frictionless cart and show that
the work done is equal to the increase in kinetic energy of the cart. Furthermore, you will show
that the increase in energy of the cart is equal to the decrease in potential energy of the falling
weight that supplies the force on the cart.
The apparatus consists of a cart that is accelerated along a linear track by the constant force due
to the tension in a cord attached to a falling mass. Three photogate timers spaced along the track
measure the time it takes for the photogate flag of the cart to pass through each timer. The speed
at that position is the flag width divided by the time measured by the photogate.
Procedure:
1. Make sure you understand and have checked the operation of the photogate timers.
2. To simulate a frictionless system, tip the track until the cart rolls toward the pulley at a
constant speed. (No forces should be acting on the cart!)
3. Measure and record the mass of the cart, Mc, and the width of the photogate flag.
4. Select a falling mass, Mf between 0.05 kg and 0.20 kg. With the string and weight attached,
record xf the position of the cart’s flag on the track when the falling mass hits the floor. After
this point the string becomes slack and does no more work. Space the three photogate timers
at equal intervals along the portion of the track traveled under the influence of the tension in
the string. Record these positions and the corresponding flag position x0 from which you
release the cart from rest.
5. With all masses and photogate positions recorded, place the cart at the starting position. Set
the photogate timers to “gate” mode; reset the timers; load the string with your particular
falling mass, and release the cart. Record the three photogate time intervals in your data
table. Repeat this data run at least two more times to check the reproducibility of the
apparatus. Use these values to estimate the uncertainty in t.
Each student should record individual data using a different falling weight. Do not share data.
