# Nonuniform circular motion/fricton?

A toy train rolls around a horizontal 1.0 m diameter track. The coefficient of rolling friction is 0.10. How long does it take the train to stop if it's released with an angular speed of 26 rpm?

### 1 Answer

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- billrussell42Lv 72 months ago
1 rev = πd = 3.14 m

26 rev/min x 3.14 m/rev x 1min/60s = 1.36 m/s

force of friction = 0.1w = 0.1mg = 0.98m

de-acceleration = F/m = 0.98m/m = 0.98 m/s²

"How long" ? is that time or distance? assuming time

v = v₀ + at

0 = 1.36 + (–0.98)t

t = 1.39 s

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Yes, "how long" is time! Thank you for your help! :)