Friday
May 6, 2016

# Homework Help: physics

Posted by james on Wednesday, June 13, 2007 at 7:49pm.

find the average of a block being propelled propelled by an elastic band.

very sorry to disturb Mr bobpurlsey again. i am very thankful to you replies. the only problem that lies in the answer is that i haven't been taught hooke's law in Grade 11. which indicates 1/2kx^2 i looked this up in wikipedia but did not learn this in grade 11. is there any other way to attempt this question sir? i know the force applied in the elastic band is not constant because it changes as the elastic destreches. just to let you u know i get an extra wooden block with a small edge on it to hook the elastic and propell the other block. sir is there any other way i can understand this. links?
thank you very very much for all your help

This is very odd that you haven't had Hookes'Law. Normally, that is in about 8th grade science. Anyway, it explains the force not being constant on the rubber as expansion changes (force=kx).

No, I dont think you will be able to do it any other way, Unless you have an electronic doppler velocity detector to detect how fast the block is going at release.

I am really wondering if you are certain in your mind what you are doing. The sentence starting this out says "find the average of a block being propelled by an elastic band". Hmmm. Average what? I thought you were looking for the force of friction after it was released and was sliding.

You can learn about Hookes law by reading it yourself. Rubber bands are not truly elastic, but they are close.

yes i am trying to average find force of friction.

well, all I can say is that the average force of friction does not depend on the rubber band. What you are doing is measuring the friction by how far the block slides, and that depends on the rubber band. Reread my posts on this.