# Galilean transformation problem (Speed)

**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?

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