# Basic Newton's Laws and Applied Force: 3 boxes

• cassie123
In summary, three boxes with masses of 10 kg, 20 kg, and 30 kg are in contact on a frictionless horizontal surface. A horizontal force of 90 N is applied to the first box. The acceleration of the three boxes is 1.5 m/s^2. The net force on the first, second, and third box are 15 N, 30 N, and 45 N, respectively. The contact forces between the first and second box is 75 N, and between the second and third box is 45 N. The contact forces are a result of each box pushing against the other boxes in the system.
cassie123

## Homework Statement

Three boxes are in contact with each other on a frictionless horizontal surface as shown. The masses of the boxes are m1 = 10 kg, m2 = 20 kg, and m3 = 30 kg. A horizontal force F = 90 N is applied to m1.
Calculate:
a. the acceleration of the three boxes.
b. the net force on each box.
c. the contact forces between the boxes.

## Homework Equations

Newtons second law
F=ma

## The Attempt at a Solution

total mass = 60 kg
F = ma

1) a = F/m = 90/60 = 1.5 m/s^2

2) net force on each box
F1 = m1a = 10*1.5 = 15N
F2 = m2a = 20*1.5 = 30 N
F3 = m3*a = 30 *1.5 = 45 N

Am I missing forces in calculating the net force?

c) contact force
90-15 = 75 N btwn 1st and 2nd box
75- 30 = 45 N btwn 2nd and 3rd box

The above is my best guess although I am not confident that this is the way to calculate contact forces. (What are contact forces?) Should I be using something like f=(F*(m2+3))/(m1+(m2+3) or f=(F*m2)/(m1+m2) to find the contact force between boxes 1 and 2?

Theres a two force which affects first two boxes (m1 and m2).But there's only one force effects third box which is contact between m2 and m3.Contant force means If you push m1 the force will affect the system and in the system m1 will push m2.But every force has a opposite force so m2 applies force on m1.
For this problem,If you want to answer question quick,start with the last box.Theres one force act it.Find that force.

After find that force think this way.
Theres one box in the middle which its m2.Now there's two forces acting on it the contant force between m2 and m3 and contant force between m1 and m2.And their net force will be m2a=F which its 30N.

To this solution step by step.Youll find the answer

cassie123 said:
The above is my best guess although I am not confident that this is the way to calculate contact forces.

You should be more confident as you've got the solution precisely correct.

I did not notice you were right.What a shame for me

PeroK said:
You should be more confident as you've got the solution precisely correct.

So it's right as shown? Never mind the other guesses for contact force? Thanks so much!

RyanH42 said:
Theres a two force which affects first two boxes (m1 and m2).But there's only one force effects third box which is contact between m2 and m3.Contant force means If you push m1 the force will affect the system and in the system m1 will push m2.But every force has a opposite force so m2 applies force on m1.
For this problem,If you want to answer question quick,start with the last box.Theres one force act it.Find that force.

After find that force think this way.
Theres one box in the middle which its m2.Now there's two forces acting on it the contant force between m2 and m3 and contant force between m1 and m2.And their net force will be m2a=F which its 30N.

To this solution step by step.Youll find the answer

## 1. What are Newton's three laws of motion?

Newton's first law states that an object at rest will remain at rest and an object in motion will remain in motion at a constant velocity unless acted upon by an unbalanced force. Newton's second law states that the acceleration of an object is directly proportional to the net force acting on it and inversely proportional to its mass. Newton's third law states that for every action, there is an equal and opposite reaction.

## 2. How are Newton's laws applied in everyday life?

Newton's laws are applied in everyday life in many ways, such as in driving a car (acceleration and braking), playing sports (force and motion), and even in simple tasks like walking (equal and opposite reaction forces from the ground).

## 3. Can you explain the concept of inertia in relation to Newton's laws?

Inertia is the tendency of an object to resist a change in its state of motion. This concept is related to Newton's first law, as it explains why objects will stay at rest or continue moving at a constant velocity unless acted upon by an unbalanced force.

## 4. How do forces affect the motion of objects?

Forces can cause an object to accelerate, decelerate, or change direction. According to Newton's second law, the net force acting on an object will determine its acceleration, and the direction of the force will determine the direction of the acceleration.

## 5. What is the difference between mass and weight in Newton's laws?

Mass is the measure of an object's inertia, or its resistance to acceleration, while weight is the measure of the force of gravity acting on an object. This means that an object's mass will remain constant regardless of its location, while its weight will vary depending on the strength of the gravitational force at that location.

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