Passage VI

The total mechanical energy (TME) of an object is defined as the sum of its potential energy (energy of position, abbreviated PE) and its kinetic energy (energy of motion, abbreviated KE). The object's PE = mgh, where m is its mass, h is its height above an arbitrary reference point, and g is the acceleration due to gravity (9.8 m/see²).The object's KE = mv²/2, where v is its velocity.

When the object's motion changes but the sum KE+PE does not change, the TME is said to be conserved.

A group of students performed 2 experiments to investigate the conservation of TME.

Experiment 1

Starting from rest at Point P (see Figure 1), a 1 kg toy cart was released and allowed to move along a frictionless track in an airless vacuum chamber.

At various points along the track, the students determined both the cart's KE and PE in joules, J (see Table 1) .

Experiment 2

The students performed an experiment in air at atmospheric pressure using the cart from Experiment 1 and the track shown in Figure 2; this track was NOT frictionless.

On this track, Positions W and Y were at the same altitude; the altitude at Positions U, V, and Z was zero. The cart was launched at Position U with a given KE, after which the students did not interfere with the cart's motion. The cart had to have enough KE between Positions W and Y to prevent the cart from falling away from the track.

(Note: The results of Experiment 2 are not provided; some of the questions will ask you to decide what those results most likely were. )