# Kinetic energy and work relationship problems

### Work and energy

In solving work problems, one must always be aware of this definition - theta is Combining the equations for power and work can lead to a second equation There are two forms of mechanical energy - potential energy and kinetic energy. Solutions to problems on work and energy. S10 Click here to read the question. We'll use the abreviation KE to refer to kinetic energy. a. Learn what kinetic energy means and how it relates to work. There are a couple of interesting things about kinetic energy that we can see from the equation.

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.

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.

### What is kinetic energy? (article) | Khan Academy

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. These habits are described briefly here. If needed, they sketch a simple diagram of the physical situation to help visualize it. They equate given values to the symbols used to represent the corresponding quantity e. Where needed, they perform the needed conversion of quantities into the proper unit.

### Solutions to problems on work and energy

After 50 m, the car is at rest, so its KE is zero. The total work done on the car the work done by the net force equals the change in KE. The force on the car causing it to stop is applied at the only point of contact the car has -- the ground! The ground pushes on the car opposite to the car's motion that's the meaning of the minus sign abovecausing it to stop.

You can tell this, because a car's tires get hot from the friction forces between them and the road. The KE of the cars motion is turned into heat energy the car's tires, the brakes and the road get hot so the work done on the car is not recoverable.

S11 Click here to read the question a.

## Solutions to problems on work and energy

The ball's potential energy PE gets smaller by an amount Mgh, where h is the height through which it falls 10 m. This energy change results from the work done on the ball by gravity. We can find the speed in one of two ways. If you pick a book off the floor and put it on a table, for example, you're doing positive work on the book, because you supplied an upward force and the book went up.

## Kinetic Energy

If you pick the book up and place it gently back on the floor again, though, you're doing negative work, because the book is going down but you're exerting an upward force, acting against gravity. If you move the book at constant speed horizontally, you don't do any work on it, despite the fact that you have to exert an upward force to counter-act gravity.

**Physics, Kinetic Energy, An Explanation**

Kinetic energy An object has kinetic energy if it has mass and if it is moving. It is energy associated with a moving object, in other words. For an object traveling at a speed v and with a mass m, the kinetic energy is given by: The work-energy principle There is a strong connection between work and energy, in a sense that when there is a net force doing work on an object, the object's kinetic energy will change by an amount equal to the work done: Note that the work in this equation is the work done by the net force, rather than the work done by an individual force.

Gravitational potential energy Let's say you're dropping a ball from a certain height, and you'd like to know how fast it's traveling the instant it hits the ground. You could apply the projectile motion equations, or you could think of the situation in terms of energy actually, one of the projectile motion equations is really an energy equation in disguise. If you drop an object it falls down, picking up speed along the way.

This means there must be a net force on the object, doing work. This force is the force of gravity, with a magnitude equal to mg, the weight of the object.

The work done by the force of gravity is the force multiplied by the distance, so if the object drops a distance h, gravity does work on the object equal to the force multiplied by the height lost, which is: An object with potential energy has the potential to do work.