The article focuses on the experimental setup for momentum conservation during the collision of two small balls at the end of an inclined groove in the latest version of the Peoples Education Press Selective Compulsory One textbook. It is divided into two cases: when the incident small iron ball contacts or does not contact the bottom of the track groove, and derives the relative increase in the velocity of the small iron ball exiting the horizontal groove after rolling and sliding motion after colliding with a small stationary glass ball at the groove end (relative to the ideal case without friction), as well as the system relative error for this momentum conservation experiment. Theoretical calculation results indicate that the values of both are generally large, with larger values observed when the incident small iron ball is not in contact with the bottom of the track groove. The experimental error results for the incident small iron ball not contacting the bottom of the track groove are roughly consistent with the corresponding theoretical error results, both of which show that there is indeed a significant systematic error in this experimental device in the latest version of the textbook. It is recommended to replace it with a complete collision experimental device available on the market, which has been tested to have a relative error of only ±2%.