- #1

SA32

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"A cyclist competes in a one-lap race around a flat, circular course of radius

*r*. Starting from rest and speeding up at a constant rate throughout the race, the cyclist covers the entire course in a time

*Δt*. The mass of the bicycle (including the rider) is

*m*. What is the magnitude of the net force

*F*acting on the bicycle as it crosses the finish line?

_{net}Find

*F*, the magnitude of the net force acting on the cyclist at the finish line.

_{net}Express the net force in terms of

*r*,

*Δt*,

*m*, and

*π*."

My thinking was as follows:

In circular motion,

*F*=

_{net}*F*= mv

_{centripetal}^{2}/Δt

I also know that v=2πr/Δt

Substituting the latter equation into the former, I get (m*4π

^{2}r)/Δt

^{2}

However, I am being told that my answer is "off by a multiplicative factor". I worked through a series of hints for this problem with a friend, only to come up with the same answer. Any help is appreciated!