# Kinetic energy and work relationship on job

### Work, Energy and Power

Kinetic energy is a scalar. The units are the same as for work (i.e. Joules, J). Relation bewteen KE and W: The work done on an object by a net force equals the. Kinetic energy can be defined as the capacity of an object to do work by virtue of its motion. Learn formula, equation & examples of Kinetic Energy in detail. Here we learn what work and energy mean in physics and how they are related. amount of energy associated with it; this is known as kinetic energy. .. This means that a more general equation for the work done on the box by a force at an .. Yet, we know from our experience that we get tired when doing the same job.

For instance, if you solve for the work done and you get positive joules, it means that the force gave something joules of energy. So if you have a way of determining the amount of energy that something gains or loses, then you have an alternate way of finding the work done, since the work done on an object is the amount of energy it gains or loses.

For instance, imagine a kilogram skateboarder that starts at rest. If a force starts the skateboarder moving at 10 meters per second, that force did work on the skateboarder since it gave the skateboarder energy.

### What are energy and work? (article) | Khan Academy

The amount of kinetic energy gained by the skateboarder is 2, joules. That means that the work done by the force on the skateboarder was positive 2, joules. It's positive because the force on the skateboarder gave the skateboarder 2, joules.

**Work and Energy**

If a force gives energy to an object, then the force is doing positive work on that object. And if a force takes away energy from an object, the force is doing negative work on that object.

## What are energy and work?

Now imagine that the skateboarder, who's moving with 10 meters per second, gets stopped because he crashes into a stack of bricks.

The stack of bricks does negative work on the skateboarder because it takes away energy from the skateboarder. To find the work done by the stack of bricks, we just need to figure out how much energy it took away from the skateboarder.

Since the skateboarder started with 2, joules of kinetic energy and ends with zero joules of kinetic energy, it means that the work done by the bricks on the skateboarder was negative 2, joules. It's negative because the bricks took away energy from the skateboarder.

## Mechanics: Work, Energy and Power

In this set of problems, we will be most concerned with the stored energy due to the vertical position of an object within Earth's gravitational field. Kinetic energy is defined as the energy possessed by an object due to its motion.

An object must be moving to possess kinetic energy. The amount of kinetic energy KE possessed by a moving object is dependent upon mass and speed.

- Work as the transfer of energy

The total mechanical energy possessed by an object is the sum of its kinetic and potential energies. Work-Energy Connection There is a relationship between work and total mechanical energy. The final amount of total mechanical energy TMEf possessed by the system is equivalent to the initial amount of energy TMEi plus the work done by these non-conservative forces Wnc. The mechanical energy possessed by a system is the sum of the kinetic energy and the potential energy.

Positive work is done on a system when the force doing the work acts in the direction of the motion of the object. Negative work is done when the force doing the work opposes the motion of the object.

When a positive value for work is substituted into the work-energy equation above, the final amount of energy will be greater than the initial amount of energy; the system is said to have gained mechanical energy. When a negative value for work is substituted into the work-energy equation above, the final amount of energy will be less than the initial amount of energy; the system is said to have lost mechanical energy.

There are occasions in which the only forces doing work are conservative forces sometimes referred to as internal forces. Typically, such conservative forces include gravitational forces, elastic or spring forces, electrical forces and magnetic forces.

When the only forces doing work are conservative forces, then the Wnc term in the equation above is zero. In such instances, the system is said to have conserved its mechanical energy. The proper approach to work-energy problem involves carefully reading the problem description and substituting values from it into the work-energy equation listed above.

Inferences about certain terms will have to be made based on a conceptual understanding of kinetic and potential energy.

### Work as the transfer of energy (video) | Khan Academy

For instance, if the object is initially on the ground, then it can be inferred that the PEi is 0 and that term can be canceled from the work-energy equation. In other instances, the height of the object is the same in the initial state as in the final state, so the PEi and the PEf terms are the same. As such, they can be mathematically canceled from each side of the equation.

In other instances, the speed is constant during the motion, so the KEi and KEf terms are the same and can thus be mathematically canceled from each side of the equation. Finally, there are instances in which the KE and or the PE terms are not stated; rather, the mass mspeed vand height h is given. In such instances, the KE and PE terms can be determined using their respective equations. Make it your habit from the beginning to simply start with the work and energy equation, to cancel terms which are zero or unchanging, to substitute values of energy and work into the equation and to solve for the stated unknown.

Habits of an Effective Problem-Solver An effective problem solver by habit approaches a physics problem in a manner that reflects a collection of disciplined habits. While not every effective problem solver employs the same approach, they all have habits which they share in common.