# mPEC Forum

## ฟิสิกส์โอลิมปิก วิทยาศาสตร์โอลิมปิก ข้อสอบแข่งขัน ข้อสอบชิงทุน => GRE - Physics => Topic started by: conantee on December 31, 2009, 11:06:44 AM

 Title: GR8677.021 Post by: conantee on December 31, 2009, 11:06:44 AM 21. Two observers and observes two events, A and B. The observers have a constant relative speed of . In units such that the speed of light is , observer obtained the following coordinates:      Event A:       Event B: What is the length of the space-time interval between these two events, as measured by ?(A) (B) (C) (D) (E) Title: Re: GR8677.021 Post by: conantee on December 31, 2009, 11:53:43 AM First, the space-time interval is independent of observer. So, don't worry about the speed of observer .Next, let's calculate the space-time interval between two events. You should know that space and time are treated differently. Instead of usual cartezian coordinates, time is treated in imaginary axis. The "distance" in space-time is then can be calculated from: where speed of light is In our problem Hence, . So, .The answer is (C). 24 of 100 people got the right answer.