Jen's phone uses a simple algorithm to count the number of strides she takes. The algorithm looks at the phone's accelerometer measurements, and counts a stride each time the acceleration goes from below to above $3$ g. Based on the number of strides counted in the $20$-second window shown here, and assuming that Jen travels $140$ cm per stride, what was Jen's average walking speed, in meters per second, over the $20$-second window? Express your answer as a decimal to the nearest hundredth.

 Nov 16, 2022

We need meters per second, not centimeters per second, so convert the stride of 140 cm to meters:

140 cm times 1 m/100 cm = 1.4 meters.

The number of pulses going above the dashed line for the 3 g threshold to

count as strides are 19. Therefore, a total assumed distance of $19 times 1.4 meters  is covered in 20 seconds, making the average speed

19 times 1.4/20 = 19 times 0.07 = 1.33m/s. smiley

 Apr 18, 2023

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