On the student pilot's sixth practice landing approach, he pulled the throttle back and the engine went to full power. He pulled the mixture control out to stop the engine running at full power. He set up best glide speed and determined that for the conditions present that the "approach would fall short of the runway." The wheels impacted electric wires and the airplane came to rest inverted. Federal Aviation Administration Inspectors examined the wreckage and found that the throttle cable end separated from the linkage.