Angle has bought a bicycle speedometer/odometer. It is a magnetic device attache

Question

Angle has bought a bicycle speedometer/odometer. It is a magnetic device attached to the spokes of the front wheel, and a sensor mounted on the fork which measures each passage of the magnet. From the rate at which the device passes the sensor (rotations per second), a small computer can then calculate the bicycle's forward speed (in m/s) and distance traveled (in m). etc. Unfortunately, Angie threw away the manual as soon as she opened the box. After attaching the sensor and magnet, she turns the small computer on, and is surprised when it blinks "RADIUS = ?" and prompts her to enter a number in centimeters. "It must be asking for the radius of the wheel." she says. "No." says Bob, "it's asking for the distance from the center of the wheel to the magnet, where it's located on the spokes." Who is correct? Explain your answer.

Explanation / Answer

Now, the magnet would pass the sensor n times per second (assume)
angular velocity w = n*2*pi rad/s
Forward speed = w*(radius of the tyre)
Distance travelled = w(radius of wheel)*t

hence the computer was asking for the radius of the bicycle tyre

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