Physics Problem that would stump the smartest!

[J0hnny]

I need to calculate the torque required to move a 100lb person on a wheel that is 4 inch. in diameter. (Scooter)

The way I calculated:

I used the simple F=(coefficient of rolling friction)(Normal Force)
F=(0.015 for wheel)(50lbs)
F=0.75lbs

Torque=Force* Distance
Torque=0.75*(4in./12ft)
Torque=0.25lb*ft
this torque I am assuming that the person has already started moving and the torque required to continue movement.

Am I correct to assume a rolling friction coefficient? If I use the kinectic friction coefficient of 0.8, then I would get ~13lb*ft of torque.

 

[Luden]

I could ask, I'm in class now. But instead i lurk atot...

 

[PullMyFinger]

It depends on how realistic you want the answer to be.

For example, what is the wheel made out of? A rolling coefficient of 0.015 sounds like you are assuming a solid/hard material. Can you assume any wheel material, say an inflated rubber tire, or are you given certain criteria?

Next, you should probably assume some loss from the wheel bearings. Most roller bearings are in the 0.001 - 0.005 coefficient of rolling friction.

Other than that, you seem to be on the right track. Don't forget, the numbers you have derived so far are only for one wheel, you will need to double that number for two wheels.

 

[her209]

If you are assuming the person and scooter is already in motion, then the inertia factor is of no concern. You are only concern with keeping the person and scooter going at a constant speed, am I correct? So find out the amount friction force that is applied to the wheel contacts with the ground. The frictional force is dependent on the total weight of the person and scooter and the surface area contact of the wheels with the ground.

 

[Yossarian]

wouldn't your moment arm be 2" if the wheel diameter is 4"?

 

[J0hnny]

Ahhh, it would be 2"

 

[B00ne]

hmmm physics is alot easier when one uses scientific (SI) units instead of these weird ones - I heard it makes space probes reach their destination too

is the person standing on the wheel? and the wheel is horizontally? if so where is the person satnding in the center or the rim.

also if the wheel is not moving u would need the sticking coefficiant of friction and yes u use only the radius as the measure for the lever