# Two block on each other with friction

• Sarah00
In summary, the conversation discusses a problem involving two masses and their forces, specifically the friction force and the normal force. The attempted solution is to use the equations F = ma and Ffr = u * Fn to calculate the forces, but the individual's solution is incorrect. The expert then asks the individual to consider the correct values for the normal force and the direction of the friction force.
Sarah00

F = ma
Ffr = u * Fn

## The Attempt at a Solution

After drawing FBD
For m2: we have only friction force in horizontal axis so Ffr = ma ==> u * Fn = ma ==> u * mg = ma ==> u * g = a ==> a = 0.5 * 10 = 5 m/s2
Now, moving to m1:
F - Ffr = ma ==> F - u Fn = 10 * 5 ==> F - 0.5*130 = 50 ==> F - 65 = 50 ==> F = 115 N

But it is not in choices,

Is my solution wrong?
or
Are the choices wrong?

One of the choices is right. Your solution is wrong.

a = Fnet/m

What mass is needed in this equation?

Sarah00 said:
Now, moving to m1:
F - Ffr = ma ==> F - u Fn = 10 * 5 ==> F - 0.5*130 = 50

Did you use the correct value for the normal force here?

I though that the mistake is with the Fn.
Fn here is the sum of two weights as net vertical force is zero

Dr Courtney, you considered them as single mass I see. The answer will be 65 N then. but I want to know my mistake

Sarah00 said:
I though that the mistake is with the Fn.
Fn here is the sum of two weights as net vertical force is zero

Think about whether the friction force acting on m1 is coming from m2 or coming from the ground.

What is the normal force acting between m1 and m2?

## What is the concept of "Two block on each other with friction"?

This concept refers to a system where two blocks are stacked on top of each other and are in contact with each other. This system is affected by the force of friction between the two blocks, which can cause them to either move or remain stationary.

## How is friction calculated in this system?

Friction in this system is calculated using the formula F = μN, where F is the force of friction, μ is the coefficient of friction, and N is the normal force between the two blocks. The coefficient of friction depends on the materials of the two blocks and the surface they are in contact with.

## What factors affect the motion of the two blocks?

The motion of the two blocks is affected by the force of gravity, the normal force between the two blocks, and the force of friction. The weight of the blocks, the angle of inclination, and the coefficient of friction also play a role in determining the motion of the blocks.

## Can the two blocks be in equilibrium with each other?

Yes, the two blocks can be in equilibrium if the forces acting on them are balanced. This means that the force of friction must be equal and opposite to the force of gravity and the normal force. In this case, the blocks will remain stationary and will not move.

## What is the difference between static and kinetic friction in this system?

Static friction is the force that prevents the two blocks from moving when they are at rest. Kinetic friction, on the other hand, is the force that opposes the motion of the blocks when they are in motion. The coefficient of static friction is usually higher than the coefficient of kinetic friction in this system.

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