Minimum Coefficient of static friction to keep a block from sliding?

In summary, the problem involves a 5kg block on top of a 15kg block on a frictionless table, with a roughened surface between them to prevent slipping. A 40N horizontal force is applied to the top block and the minimum coefficient of static friction needed to prevent slipping is being sought. The first attempt to solve using F=ma and f=mewFN resulted in a value of .2, but the correct answer is actually .6. A second attempt to incorporate the 40N force resulted in the correct answer of .61.
  • #1
Brodo17
18
0
A 5kg block is placed on top of a 15kg block that rests on a frictionless table. The surface between the top and bottom blocks is roughened so that there is no slipping between the blocks. A 40N horizontal force is applied to the top block. What is the minimum coefficient of static friction necessary to keep the top block from slipping on the bottom block?


F=ma
f=mew FN


Ok, in my first attempt I figured that if the blocks don't slide apart, then the entire sysstem would be accelerating. I said 40N = (20)a, and found that a=2m/s^2
Using this I said (5kg)(2m/s^2) = mew FN
10 / (9.8 X 5) = .20

However the answer says that it is actually .6

Then I though that maybe the system could not accelerate at all because the opposing frictional force will stop it from accelerating.
Im not even sure if I am on the right track though, and I cannot figure this out!

Thank you!
 
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  • #2
"Using this I said (5kg)(2m/s^2) = mew FN"

You forgot the 40 N pulling force.

ehild
 
  • #3
What do you mean I forgot about the 40N force? Where would I put it in my equation?

Actually, If I go
(5kg)(2) = mewFN + 40N
-30N = mewFN
-30 / (-9.8 x 5) = .61

Thanks
 

Related to Minimum Coefficient of static friction to keep a block from sliding?

What is the minimum coefficient of static friction?

The minimum coefficient of static friction is the minimum amount of friction between two surfaces that is needed to prevent one surface from sliding or moving relative to the other.

How is the minimum coefficient of static friction determined?

The minimum coefficient of static friction is determined by dividing the maximum force of static friction by the perpendicular force applied to the surface. This ratio is also known as the coefficient of static friction.

What factors affect the minimum coefficient of static friction?

The minimum coefficient of static friction can be affected by the type of surface materials, the surface roughness, the angle of the surface, and the weight or force applied to the surface.

What is the importance of the minimum coefficient of static friction?

The minimum coefficient of static friction is important in determining the stability and safety of structures and objects. It helps prevent objects from slipping or sliding on surfaces, which can cause accidents or damage.

How does the coefficient of static friction differ from the coefficient of kinetic friction?

The coefficient of static friction is the maximum amount of friction needed to keep an object at rest, while the coefficient of kinetic friction is the amount of friction between two surfaces when one is in motion. The coefficient of kinetic friction is typically lower than the coefficient of static friction.

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