# Why Is Kinetic Energy Zero for the 4kg Carriage in This Problem?

• pyroknife
In summary, The problem involves using potential energy and kinetic energy to solve for the motion of a 6kg object attached to two links. The solution involves setting the sum of all the forces equal to 0 and solving for the velocity. However, there is some confusion about the kinetic energy of the 4kg carriage, which appears to be 0 even though it is still moving. The question also asks about the freedom of movement of the object when the links are in a straight line.
pyroknife
I attached the problem and the solution.

The book uses V has potential energy and T as KE.

I'm not quite sure how they did this problem. I was following it until the 2nd to last line of equations. where they have "8.829-11.772+1/2*6*v^2+0=0"
Why don't they have the KE for the 4kg carriage? It looks like they said that was 0, but isn't that still moving too?

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pyroknife said:
I attached the problem and the solution.

The book uses V has potential energy and T as KE.

I'm not quite sure how they did this problem. I was following it until the 2nd to last line of equations. where they have "8.829-11.772+1/2*6*v^2+0=0"
Why don't they have the KE for the 4kg carriage? It looks like they said that was 0, but isn't that still moving too?

What freedom does it have to move when (at the instant) the links are inline?

## 1. What is the law of conservation of energy?

The law of conservation of energy is a fundamental principle in physics that states that energy cannot be created or destroyed, but can only be transferred or transformed from one form to another. This means that the total amount of energy in a closed system remains constant.

## 2. What are the different forms of energy?

There are many different forms of energy, including kinetic energy (energy of motion), potential energy (stored energy), thermal energy (heat energy), chemical energy (energy stored in bonds between atoms), and electromagnetic energy (energy in the form of light, radio waves, etc.).

## 3. How is the law of conservation of energy applied in everyday life?

The law of conservation of energy is applied in many everyday situations, such as turning on a light bulb (electrical energy is converted to light energy), riding a bike (muscular energy is converted to kinetic energy), and cooking food (chemical energy in the food is converted to thermal energy).

## 4. Can energy be converted from one form to another without any loss?

No, energy conversions are never 100% efficient. Some energy is always lost in the form of heat or other forms of energy. This is known as energy dissipation or entropy.

## 5. How does the law of conservation of energy relate to the concept of perpetual motion?

The law of conservation of energy states that energy cannot be created or destroyed, so a perpetual motion machine (a machine that would run forever without any input of energy) is impossible. This is because the machine would have to create energy, which goes against the law of conservation of energy.

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