How Do Friction and Surface Affect Block Acceleration in a Pulley System?

[joel amos]

Homework Statement

http://imageshack.us/a/img703/7864/physicsb.png
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?

 

[howie8594]

What do you think the acceleration would be?

 

[tiny-tim]

hi joel!

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

 

[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?

 

[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.

 

[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 ​

 

[joel amos]

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