# Torque problem

1. Nov 7, 2005

### leezak

The figure shows a bicycle wheel resting against a small step whose height is h = 0.110 m. The weight and radius of the wheel are W = 29.0 N and r = 0.350 m. A horizontal force F is applied to the axle of the wheel. As the magnitude of F increases, there comes a time when the wheel just begins to rise up and loses contact with the ground. What is the magnitude of the force when this happens?

I drew a diagram, yet i'm not even sure how to start this problem... help please! thanks!

2. Nov 7, 2005

### whozum

What direction is the normal force from the step acting? What component is vertical? How will this affect the normal force on the ground?

3. Nov 7, 2005

### leezak

the normal force from the step is acting horizontally towards the wheel and the vertical components are the weight (29 N) and the Normal force from the ground. what do i do with this info? do i somehow incorporate the torque equation?

4. Nov 7, 2005

### whozum

Since the step is not applying a force towards the center of mass, there is a torque created about the step. You step therefore applies an upwards force on the tire too. That's the one I asked you to find.

5. Nov 7, 2005

### whozum

Last edited by a moderator: Apr 21, 2017
6. Nov 7, 2005

### leezak

i'm not sure how to find that

7. Nov 7, 2005

### leezak

okay so i got that the angle is 34.44 degrees and that the force going up is (Normal force of the step)(sin34.44) right? am i then supposed to find the sum of the forces or something?

8. Nov 7, 2005

### whozum

Yup so for the wheel to start moving up, it needs to have a net force in the upward direction. From your FBD you ahve the force of gravity and now the Normal force of the step, so these are your vertical forces. Under what condition will the net force be upwards?