# Forces btwn Boxes: Find Acc & Magnitude of Contact Forces

• pb23me
In summary, the problem involves three boxes (m1=20kg, m2=40kg, m3=25kg) connected and placed on a frictionless surface. The applied force to box 3 is 75 Newtons, causing all three boxes to accelerate with a magnitude of 0.88 m/s^2. The contact forces between the boxes are not all the same, with the force of box 2 on 3 being 53N and the force of box 3 on 2 being 22N. The net force is always in the direction of the acceleration.
pb23me

## Homework Statement

boxes 1,2 and 3 are touching each other. a force is applied to box 3. assume that the surface is frictionless. the masses are m1 20 kgs, m2 is 40 kgs, and m3 is 25kgs. the applied force to box 3 is 75 Newtons. find te acceleration of the blocks and the magnitude of there contact forces.

Fnet=ma

## The Attempt at a Solution

box 3 has applied force of 75N and and opposite normal force of 75N?? not sure what the value of the other horizontal forces are?? also not sure where to include the weight of the boxes??

#### Attachments

• Hmwk5a[1].pdf
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I think I've figured the problem out just not sure if the contact forces are all the same magnitude?

pb23me said:
I think I've figured the problem out just not sure if the contact forces are all the same magnitude?
Please show your work. You first need to look at the entire system of 3 boxes to solve for the acceleration using Newton 2. Then look at each box separately in a free body diagram, noting any contact normal or applied forces in the x direction, and use Newton 2 again for each box. They all move together, so each has the same acceleration. The contact forces are not the same.

i considered the whole system as one unit. added the masses to get mass 85kgs. Fnet= 75N then found acceleration = .88 m/s^2. i used the accleration and mass of box 3 to determine the force of box 3 acting on box 2 F3=22N now how do i find the other contact forces?

am i correct in saying that the force applied on box 2 from box 3 is 22N or is that the net force?

When you looked at block 3, the force you solved, 22 N , was the NET force acting on block 3. Since Block 3 has an applied force of 75 N acting left, then the normal force of 2 on 3 must be __?___ in which direction? Then try the same approach using Block 1.

idk the contact force is 53N so assume it would be -53N of 2 on 3.

What do you mean by the minus sign? If the 75 N force acts left, the 53 N force of 2 on 3 must act right. The net force (22N) is always in the direction of the acceleration (in this case, F_net acts left).

## 1. What is the definition of "forces between boxes"?

Forces between boxes refer to the interactions or pushes or pulls between two boxes that are in contact with each other. These forces can be caused by a variety of factors, such as gravity, friction, or external forces applied to the boxes.

## 2. How do you find the acceleration of contact forces between boxes?

The acceleration of contact forces between boxes can be found by using Newton's Second Law, which states that the net force on an object is equal to its mass times its acceleration. By calculating the net force acting on the boxes, the acceleration can be determined using the formula a = F/m, where a is acceleration, F is net force, and m is mass.

## 3. What factors affect the magnitude of contact forces between boxes?

The magnitude of contact forces between boxes can be affected by several factors, such as the weight and mass of the boxes, the surface material and texture of the boxes, and the presence of external forces, such as friction or applied forces.

## 4. How do you calculate the magnitude of contact forces between boxes?

The magnitude of contact forces between boxes can be calculated by first determining the net force acting on the boxes, and then using the formula F = ma, where F is force, m is mass, and a is acceleration. By plugging in the known values, the magnitude of the contact forces can be determined.

## 5. Why is it important to calculate the forces between boxes?

Calculating the forces between boxes is important for understanding the motion and behavior of the boxes. It can also help in predicting and preventing accidents or damages caused by the boxes, as well as in designing and optimizing structures and systems that involve multiple boxes in contact with each other.

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