# Homework Help: Pulley, friction, acceleration

1. Oct 10, 2012

### joel amos

1. The problem statement, all variables and given/known data
http://imageshack.us/a/img703/7864/physicsb.png [Broken]
From the image above:
a) If there is no friction between A and surface, what is the blocks' acceleration?
b) With coefficient of 0.2?

Last edited by a moderator: May 6, 2017
2. Oct 10, 2012

### howie8594

What do you think the acceleration would be?

3. Oct 10, 2012

### tiny-tim

hi joel!

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

4. Oct 10, 2012

### joel amos

So I found acceleration to be 4.9m/s/s without friction and 3.92m/s/s with a coefficient of kinetic friction of 0.2. Is this correct?

5. Oct 10, 2012

### howie8594

4.9 $m/s^2$ is correct for the acceleration without friction. You could figure that out just by looking at the diagram because you know that if the force of gravity pulling down 1 block pulls down twice that mass, then the system will accelerate at half of the acceleration for one block. In your case, it's half of g.

For the acceleration of the block including friction, I'm not totally sure, but 3.92 $m/s^2$ sounds reasonable. You probably got it.

6. Oct 11, 2012

### tiny-tim

hi joel!

(just got up :zzz:)

yes, howie8594 is correct …

you can pretend everything is in a line …

force 9.8, mass 2, -> acceleration 4.9​

similarly for the friction µ = 0.2 …

force 9.8 * (1 - 0.2), mass 2, -> acceleration 4.9*0.8

7. Oct 11, 2012

### joel amos

Thanks a lot for your help and confmirations. Highly appreciated :)