# Finding Magnitude of Contact Forces in Boxes 1, 2 and 3

• matt@USA
In summary, the problem involves a force of 7.50N pushing three boxes with masses of 1.3kg, 3.2kg, and 4.9kg. The goal is to find the magnitude of the contact forces between the boxes. The solution involves finding the net forces on each box using F=ma, and then using a free body diagram to determine the individual contact forces. The incorrect answers may have been due to not considering all the individual forces on each mass.
matt@USA

## Homework Statement

A force of magnitude 7.50N pushes three boxes with masses m1=1.3kg, m2=3.2kg, and m3= 4.9kg as shown in the figure. I want to find the magnitude of the contact forces between boxes 1 and 2, and between boxes 2, and 3. Now, the force, 7.5N is being pushed from right to left on box m3. We are assuming that friction is irrelevant in this problem.

## Homework Equations

I know to find the acceleration, I add the three masses together, and divide the total into the force. To find the magnitude of the contact force, f12, I would simply say f2-f1. For contact force f23, I would do the same, except I would say f3-f2. I solved the problem, but when I submitted the answers, they were incorrect. CAN SOMEONE PLEASE DOUBLECHECK TO SEE IF I DID SOMETHING WRONG?

## The Attempt at a Solution

I came up with f1=-1.04N, f2=2.56N, and f3=3.92N.
f2-f1=2.56N+1.04N?

If you found F1, F2, and F3 just by using F = ma, then be warned that these are the NET forces on each mass. However, each of these net forces is the sum of all the individual forces acting on that mass. The contact force with an adjacent box is one of these individual forces. For example, for a box in between two other boxes, there will be contact force acting on it from the left, and another acting on it from the right. These two sum together to make the net force. So, in order to determine all the forces acting on each mass, start by drawing a free body diagram for each mass and solve for all the forces on each mass.

## 1. How do you find the magnitude of contact forces in boxes 1, 2 and 3?

The magnitude of contact forces in boxes 1, 2 and 3 can be found by using the laws of motion and considering the mass, acceleration, and direction of each box.

## 2. What is the importance of finding the magnitude of contact forces in boxes 1, 2 and 3?

Finding the magnitude of contact forces in boxes 1, 2, and 3 is important in understanding the overall forces acting on the system and predicting the motion of the boxes. It can also help in identifying any potential issues or risks in the system.

## 3. Are there any assumptions made when finding the magnitude of contact forces in boxes 1, 2 and 3?

Yes, when calculating the magnitude of contact forces, it is assumed that the boxes are in direct contact with each other and that there are no external forces acting on the system.

## 4. What factors can affect the magnitude of contact forces in boxes 1, 2 and 3?

The magnitude of contact forces can be affected by the mass, acceleration, and friction between the boxes. The shape and surface of the boxes can also play a role in determining the magnitude of contact forces.

## 5. Can the magnitude of contact forces in boxes 1, 2 and 3 change over time?

Yes, the magnitude of contact forces can change over time if there are any external forces acting on the system or if the mass, acceleration, or friction between the boxes changes. It can also change if the boxes move or collide with other objects.

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