Hi all, concerned Dad here - looking for a validating opinion on the following and would be eternally grateful with some guidance/help. The attachment, Unit4ExamAQ7c is from one of my son's honor's exams. He gets #7c CORRECT with the answer v=2.29 m/s. However, the teacher grades him WRONG as he claims the answer was achieved "by accident." I asked an engineer friend to review the answer and his response was "the grader got it wrong due to laziness." his response is in the attachment ReviewofPhysicsExams. Thank you VERY much!