Physics Help Needed

[Trez]

I am using the Singapore Interactive Science Volume B Theory Workbook doing revision 22. We are on question 20 which has a girl with a metre rule pivoted at its zero marking. A load of 40 N is placed at various positions along stick and we are to measure the effort required to lift the load (from the ending point of the stick). It is hard to draw but I hope this makes sense to someone. This was simple for us when we did not take into account the mass of the rule. We just calculated

 

Moment = distance from pivot to load X load and then we used algebra to ensure the Moment from pivot to the end of the stick was the same.

 

Now, the next step asks what effort would be required taking into account the mass of the rule is 10N. :confused: We are stuck....I've been searching the web but so far have found nothing. Any of you sciency types out there?

 

Thank you for any help you can give us.

[Kathy in Richmond]

One way to do this is to assume that the mass of the meter stick is a load concentrated at its center of mass. So place a load of 10 N at the midpoint of the stick and treat it in the same manner. There will be two moments now, and both are calculated in the same way: moment = distance from pivot x load. They both act to swing the pivot in the same direction, so the effort required to lift the stick will be calculated using both of the moments.

[Trez]

Thank you so much for that.....makes perfect sense and works out to the correct answer. I knew I could count on the hive to help us out! :001_smile:

[Kathy in Richmond]

Glad it worked out! I took a stab at it w/o seeing the diagram, so I was hoping it was on target. Have fun with it.:001_smile: