Angular velocity of bicycle wheel

[Nelson2436]

Homework Statement

A bicycle rider is moving with a velocity of 13.0 m/s. What is the angular velocity of his wheels if they have a diameter of 0.660m? Assume the wheels are rolling without slipping.

a) 39.4 m/s
b) 19.7 m/s
c) 39.4 s^-1
d) 4.29 s^-1
e) none of the above

Homework Equations

v = ω r

The Attempt at a Solution

ω = v/r
ω = (13m/s) / (0.330m) = 39.4 s^-1
This problem was given on a test, I put "c" and got it wrong. It seems very straightforward and I'm not sure where I went wrong. Is there a mistake in my work? I am thinking it was most likely a mistake with the grading machine but I just wanted someone to confirm before I talked to the teacher. Thanks.

 

[phyzguy]

Your answer looks correct to me.

 

[haruspex]

Yes, your answer is definitely correct. Note that you almost don't need the question. Just looking at the choice of answers, and assuming each wrong answer corresponds to a single likely error, (c) stands out as the common theme.

 

[kboyer HCC]

It's a units issue. The 39.4 technically has units of 'revolutions per second'. Divide by 2pi to get your answer in 'radians per second', which can be written as 1/second. This would make the correct result 6.27 radians per second, which matches up to 'e - none of the above'.

 

[haruspex]

The 39.4 technically has units of 'revolutions per second'.

No, dividing tangential velocity by radius gives radians per second.
Anyway, this thread is three years old.

 

[kboyer HCC]

My mistake. I did a google search related to angular velocity of bikes and when this came up, I didn't look at the date stamp. The similar problems I was working on for my class included revolutions per second in their calculation and I jumped the gun.