x Turn on thread page Beta
 You are Here: Home >< Maths

# STEP Mechanics from Siklos booklet watch

1. I have been working on a mechanics problem from the Siklos core booklet. The question is as follows:

A uniform solid sphere of radius and mass is drawn very slowly and without slipping from horizontal ground onto a step of height by a horizontal force of magnitude which is always applied to the highest point of the sphere and is always perpendicular to the vertical plane which forms the face of the step. Find the maximum value of in the motion, and prove that the coefficient of friction between the sphere and the edge of the step must exceed .

I am not sure how to show that the coefficient of friction must exceed the value stated. I got as far as showing that is equal to friction by taking moments, and even that . However, I do not know why this leads to the conclusion that , where (hence result). Normally so I thought that in this case also, but apparently this is not so. Can anybody explain this?
Attached Images

2. I haven't worked through the question, but in your notation, to prevent slipping as the question requires, we have to have that at all times, else the limiting value of friction is exceeded. I guess that gives the inequality.
3. Aside: In the diagram your direction for is incorrect. It should be in the opposite direction.
4. (Original post by atsruser)
I haven't worked through the question, but in your notation, to prevent slipping as the question requires, we have to have that at all times, else the limiting value of friction is exceeded. I guess that gives the inequality.
Thanks, that was the condition I needed.
5. (Original post by ghostwalker)
Aside: In the diagram your direction for is incorrect. It should be in the opposite direction.
You are right, of course. The diagram is straight out of the Siklos booklet. That definitely contributed to my confusion.

TSR Support Team

We have a brilliant team of more than 60 Support Team members looking after discussions on The Student Room, helping to make it a fun, safe and useful place to hang out.

This forum is supported by:
Updated: March 16, 2013
Today on TSR

### Loughborough better than Cambridge

Loughborough at number one

Poll
Useful resources

### Maths Forum posting guidelines

Not sure where to post? Read the updated guidelines here

### How to use LaTex

Writing equations the easy way

### Study habits of A* students

Top tips from students who have already aced their exams