1. The problem statement, all variables and given/known data A girl is riding a bicycle along a straight road at constant speed, and passes a friend standing at a bus stop (event #1). At a time of 60 s later the friend catches a bus (event #2) If the distance separating the events is 126 m in the frame of the girl on the bicycle, what is the bicycle's speed? 2. Relevant equations u = u' + v 3. The attempt at a solution u = u' + v can be written as: Δx/t = Δx'/t + v v = Δx/t - Δx'/t v = 0m/60s - 126m /60s v = -126 m/ 60s v = -2.1 m/s Just wondering if the negative holds any significance? I know we're talking about speed which is scalar but how come the calculation gives a negative?