How to Determine the Mass of Stacked Blocks?

[-Justin-]

Alright this problem is giving me a massive headache...I would appreciate any help that you have, I missed this the first time and am trying to figure it out now.

Two blocks are resting on a rough surface, with one on top of the other. A force, Fapplied, with magnitude 25 Newtons, is being applied on Block2 from the left, as shown in the figure below. Friction is acting between the surface and the blocks to keep them from moving. They are not moving, but they are on the verge of sliding. The coefficients of friction between Block 2 and the surface are MUs=0.2 and MUk=0.4 .

Here is a link to a picture of the problem if you have trouble understanding what I've typed.
http://img.photobucket.com/albums/v201/b16eh2/147d0b25.jpg

 

[Pandemonium]

Here's some help I hope will assist you in arriving to the answer.

Understand that, horizontally, there are three forces on block 2. Two of them are frictional force, the other is the applied force. Let the mass of block 1 be m. Now, what is the frictional force between the two blocks, and what is the frictional force between block 2 and the surface?

 

[wais]

Finding the mass of stacked block can definitely be a tricky problem, but don't worry, with a little bit of math and some problem solving skills, we can figure it out together!

First, let's break down the problem and identify what information we have. We know that there are two blocks stacked on top of each other, and a force of 25 Newtons is being applied to the top block from the left. We also know that there is friction acting between the surface and the blocks, and the coefficients of friction are given.

To find the mass of the stacked blocks, we need to use the concept of equilibrium. In other words, the forces acting on the blocks must be balanced in order for them to not move. The two main forces acting on the stacked blocks are the force of gravity and the applied force.

We can use Newton's Second Law, F=ma, to help us solve this problem. Since the blocks are not moving, we know that the net force acting on them is zero. This means that the force of gravity pulling the blocks down must be equal to the force being applied to the top block from the left.

Now, let's look at the forces acting on the top block. We have the applied force of 25 Newtons to the left, and the force of friction acting to the right. The force of friction can be calculated by multiplying the coefficient of friction (0.2) by the normal force, which is the force pushing down on the block due to gravity. We can express this as Ffriction = MUs * Fgravity.

Since we know that the force of friction is equal to the applied force, we can set these two equations equal to each other and solve for the mass of the stacked blocks. This would look like: Fapplied = Ffriction = MUs * Fgravity. We can then rearrange the equation to solve for the mass, which would be: mass = Fapplied / (MUs * g).

Plugging in the values given in the problem, we get: mass = 25 N / (0.2 * 9.8 m/s^2) = 12.76 kg. Therefore, the mass of the stacked blocks is approximately 12.76 kg.

I hope this helps you understand how to approach and solve this type of problem. Keep practicing and don't get discouraged, with time and practice, you'll become a pro at solving these types of physics