# GPE and KE correctness help

• Sonny18n
In summary, the GPE of a 2kg block 5 meters above the floor is 10J. For a 4kg stone thrown straight up reaching a height of 5 meters, its GPE at the highest point is also 10J. To give a 1kg ball 49J of GPE, it needs to be lifted to a height of 49 meters. The KE of a 4kg mass at 3 m/s is 18J, and the mass of an object with 100J of KE while moving at 5 m/s is 4kg. The equations for GPE and KE are GPE = mgh and KE = 1/2mv^2, where m

## Homework Statement

1) What is the GPE of a 2 kg block 5 meters above the floor?

2) Joe throws a 4 kg stone straight up and it reaches a height of 5 meters. What is its GPE at its highest point?

3) How high do you have to lift a 1 kg ball to give it 49 J of GPE?[/B]

4) What is the KE of a 4kg mass at 3 m/s?

5) What is the mass of an object that has 100J of KE when moving at 5 m/s?

## Homework Equations

Honestly, the only thing I understand is the GPE stuff, which I believe is to simply multiply the mass and height together. I'm not sure if KPE is just as simple.

## The Attempt at a Solution

1) 10J

2) I got 20J but it says "highest point" so I don't know if that requires a different formula.

3) Seems simple enough, I got 49 meters by dividing 49J by 1 kg.

4 and 5 and basically Kinetic energy in general is what I need help on.

Sonny18n said:
1) 10J
Sonny18n said:
2) I got 20J but it says "highest point" so I don't know if that requires a different formula.
Why would the GPE at the highest point follow a different law from the GPE at any other point?
Sonny18n said:
4 and 5 and basically Kinetic energy in general is what I need help on.
You haven't been taught any equations for KE?

## 1. What is the relationship between GPE and KE?

The relationship between gravitational potential energy (GPE) and kinetic energy (KE) is that they are both forms of energy that an object can possess. GPE is the energy an object has due to its position in a gravitational field, while KE is the energy an object has due to its motion.

## 2. How can I determine the correctness of GPE and KE calculations?

The correctness of GPE and KE calculations can be determined by using the appropriate equations and correctly plugging in the values for mass, height, and velocity. It is also important to consider the direction of the forces and the type of motion (e.g. potential or kinetic) when calculating these energies.

## 3. Can GPE and KE be negative values?

Yes, both GPE and KE can be negative values. This occurs when the object's position or velocity is in the opposite direction of the chosen reference point. For example, if the reference point for GPE is at ground level, an object below ground level would have a negative GPE value. Similarly, if the reference point for KE is at rest, an object moving in the opposite direction would have a negative KE value.

## 4. How do changes in GPE and KE affect each other?

Changes in GPE and KE are related through the law of conservation of energy, which states that energy cannot be created or destroyed, only transferred or transformed. When an object's GPE decreases, its KE increases, and vice versa. This is because the total energy of the system (GPE + KE) remains constant.

## 5. Can GPE and KE be converted into each other?

Yes, GPE and KE can be converted into each other. This is demonstrated by the concept of potential energy converting into kinetic energy and vice versa. For example, when a ball is thrown into the air, it has GPE at its highest point and KE at its lowest point. As it falls, it converts its GPE into KE, and vice versa as it bounces back up. This conversion of energy is also seen in pendulum systems and roller coasters.