1. Sep 24, 2015

### goldfish9776

1. The problem statement, all variables and given/known data
Why the moment isn't=15* 3Nm? Since we are taking moment about point O...it's 3m away from O

2. Relevant equations

3. The attempt at a solution

#### Attached Files:

• ###### IMG_20150924_140943.jpg
File size:
45.5 KB
Views:
61
2. Sep 24, 2015

### haruspex

Are you referring to the 15kNm moment that is applied? You don't multiply that by a distance. (It would give you something with units kNm2.) a force times a perpendicular distance gives a moment, but an applied moment is already a moment. Exactly where it is applied makes no difference, only its magnitude and direction matter.

3. Sep 24, 2015

### goldfish9776

ya , i knew that . But , how can be moment be applied? only force can be applied , right?

4. Sep 24, 2015

### haruspex

Are you asking as a practical matter how it is possible to apply a moment as opposed to a force? There does not need to be a way to do that. Consider turning a nut using a spanner. One can think of it as applying a torque, or as applying two equal and opposite forces along parallel but different lines of action. If you are told a moment of some specified magnitude and direction is applied, you do not need to care about how it is applied.

5. Sep 24, 2015

### goldfish9776

yes, this will only occur in the exercise , but not in daily life ?

6. Sep 24, 2015

### haruspex

I cannot think of a way to apply a torque to an object (in an inertial frame) other than by a combination of linear forces.