The student pilot was conducting solo takeoffs and landings in a Cessna 172D, on a 3,496-foot-long, 75-foot-wide, asphalt runway. During his first approach to the runway, the airplane was high, and the student pilot performed a go-around. During his second approach, the airplane touched down, and the student pilot applied the brakes. However, the engine rpm increased, and the student pilot cycled the throttle in an attempt to reduce rpm. The airplane subsequently traveled off the end of the runway and impacted a field. The student pilot's flight instructor reported that after a good landing, he observed the airplane increase speed, and the tires were smoking as the airplane departed the end of the runway. Examination of the airplane by a Federal Aviation Administration inspector did not reveal any pre-impact mechanical malfunctions. The wind was reported as calm at a nearby airport, about the time of the accident.