Tangential acceleration of a bicycle pedal

[daffy]

I'm attempting to solve a mastering physics problem, but I've seem to run into a dead-end on this problem. I've worked out my solution and I'm certain I've rounded my sig figs correctly, but mp doesn't accept the answer.

Homework Statement

An 17-cm long bicycle crank arm, with a pedal at one end, is attached to a 24-cm diameter sprocket, the toothed disk around which the chain moves. A cyclist riding this bike increases her pedaling rate from 64rpm to 95rpm in 12 seconds.

Homework Equations

α tangential = αt = α * radius
α = dω/dt

The Attempt at a Solution

a. put terms in rpm into rad/sec
ωi = 64 rpm
ωf = 95 rpm
ωi = 64 (1 rotation / 1 minute) * (2∏ rad / 1 rotation) * (1 minute / 60 sec) ≈ 6.702 rad/sec
ωf = 95 (1 rotation / 1 minute) * (2∏ rad / 1 rotation) * (1 minute / 60 sec) ≈ 9.948 rad/sec

b. calculate rotational acceleration
α = (ωf - ωi) / time difference
α = (ωf - ωi) / 12 sec
α ≈ 0.271 rad/sec²

c. calculate tangential acceleration of the pedal
αt = α * radius
αt ≈ 0.271 rad/sec² * 17 cm
αt ≈ 0.271 rad/sec² * 0.17 m
αt ≈ 0.046 m/sec²

Does anybody know what I'm doing wrong in my reasoning? Or am I not understanding the mechanics of a bicycle correctly?

Thanks in advance

 

[haruspex]

Your working all looks correct. You didn't state the actual question, e.g. what units the answer is to be in.
If it asks for three sig figs I would answer 0.0460.