# Judo Foot-Sweep Move Problem

1. Apr 26, 2012

### Batz74

1. The problem statement, all variables and given/known data
In a judo foot-sweep move, you sweep your opponent's left foot out from under him while pulling on his gi (uniform) toward that side. As a result, your opponent rotates around his right foot and onto the mat. Figure shows a simplified diagram of your opponent as you face him, with his left foot swept out. The rotational axis is through point O. The gravitational force him effectively acts at his center of mass, which is a horizontal distance d = 28 cm from point O. His mass is 70 kg, and his rotational inertia about point O is 65 kg·m2. What is the magnitude of his initial angular acceleration about point O if your pull on his gi is (a) negligible and(b) horizontal with a magnitude of 300 N and applied at height h = 1.4 m? Assume free-fall acceleration to be equal to 9.81 m/s2.

2. Relevant equations

newtons' second law of rotation

3. The attempt at a solution

2. Apr 26, 2012

### tiny-tim

Welcome to PF!

Hi Batz74! Welcome to PF!

Show us what you've tried, and where you're stuck, and then we'll know how to help!

3. Apr 26, 2012

### Batz74

Hi, and thank you. I actually have NO idea where to start i am beginner in my physics course..

4. Apr 26, 2012

### tiny-tim

start by writing out newton's second law of rotation

5. Apr 26, 2012

### Batz74

T = Ia ?

So, T = (70x14^2) x a

6. Apr 26, 2012

### tiny-tim

i don't understand

7. Apr 26, 2012

### Batz74

neither do I -_- so am i looking for rotational inertia?

Know someone interested in this topic? Share this thread via Reddit, Google+, Twitter, or Facebook