Posted by **charlie** on Wednesday, May 30, 2007 at 7:44pm.

hello,

i am having trouble with this problem.

Calculate the average force of friction acting on a wood block as it is propelled along the floor by an elastic band ?

my solution and my ideas:

What does it mean by average froce of friction?

I first weighed the peice of wood to find its mass. i then used a newton scale and pulled the elastic band 60 cm and found the force of friction which was 8n. is this force applied(8n)?did i measure the force correctly of the elastic.?i have no idea where to go from here. is there any kinetic energy involved? do i use Ek=1/2 mv^2. any suggestions would be helpful. do i time the wodeen block after i let it go and find the velocity. i am sure it is uniform acceleration.

thank you.

The force is not likely to be 8 N unless the block is constant velocity. I have no idea how you measured the friction force, so I cant comment on your method. Since force on a rubber band is proportional to length stretched, I would measure the force at 40 cm with a spring scale. That will be the approximate average force on the block.

The other way is to measure the friction on the block by pulling it at constant velocity on the floor with a spring scale, noting the retarding force on the scale. Then, pull the block back x cm, and let it go, say d cm from the zero referce point. Total distance traveled is x+ d. Work done on friction is friction force (x+d). That has to equal the average force on the block from the rubber band * x

now you can solve for the average force this way.