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e-zero

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On her way to school, a child discovered that her loonie is missing and there is a hole in her pocket. She turned back and walked 24 m east along the sidewalk. Then, she stopped for 18 s and decided to head back to school. After walking 11 m west, she found the loonie. If the child walked at a speed of 0.25 m/s, calculate,

a) her average velocity while searching for the coin?

b) her average speed while searching for the coin?

Obviously there are two parts where the student travelled.

First part:

x1=24m

v1=0.25m/s

t1=96s (after calculation)

Second part:

x2=11m

v2=0.25m/s

t2=44s (after calculation)

If I wanted to find the average velocity then I would use my velocity formula: (avg)v = (x2 - x1) / t2 - t1

but I have to be careful because writing (avg)v = (11m - 24m) / (96s - 44s) is wrong!

Is this a common mistake? Should I name my variables differently?