Kinetic Energy Equation conceptual question?

In summary, the conversation discusses the use of potential energy in energy conservation equations. It is determined that potential energy should be considered if there is a change in it, but it is not necessary when there is no change. The work done by gravity is equivalent to the change in gravitational potential energy, but the work done by friction does not have a potential energy. Potential energy is simply a way to represent the work done by a conservative force.
  • #1
scharry03
12
1
This is mostly a conceptual confusion I'm having, not a specific problem, so it didn't seem like it'd fit under homework problems.
I'm having trouble understanding when potential energy should or shouldn't be used in a energy conservation equation. When looking at a problem with a skier going down a hall, we were given his weight, initial velocity, slope of the hill, value of friction force, and distance traveled, and were asked to find his final velocity.
We found the net work done, added it to the initial kinetic energy, and found his final velocity through his final kinetic energy. We didn't use the potential energy of gravity at all, but later we have an equation that says initial and final potential energy of gravity should be on the respective sides of the equations. Why is it they weren't used for a problem of a skier skiing down a hill? Does the net work account for it?

Thanks!
 
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  • #2
scharry03 said:
I'm having trouble understanding when potential energy should or shouldn't be used in a energy conservation equation.

If there is a change in potential energy it needs to be considered. Of course, if the system is isolated and there is no change in potential energy then the kinetic energy is constant and you have a rather boring situation. If the system is not isolated the kinetic energy will change due to any net external work.

scharry03 said:
We found the net work done, added it to the initial kinetic energy, and found his final velocity through his final kinetic energy.

Right. The work done by gravity is equivalent to the (negative) change in gravitational potential energy. The work done by friction is not conservative and therefore does not have a potential energy.

Potential energy is just a convenient way to represent the work done by a conservative; if you find the net work this will equal the change in kinetic energy.
 
  • #3
brainpushups said:
If there is a change in potential energy it needs to be considered. Of course, if the system is isolated and there is no change in potential energy then the kinetic energy is constant and you have a rather boring situation. If the system is not isolated the kinetic energy will change due to any net external work.
Right. The work done by gravity is equivalent to the (negative) change in gravitational potential energy. The work done by friction is not conservative and therefore does not have a potential energy.

Potential energy is just a convenient way to represent the work done by a conservative; if you find the net work this will equal the change in kinetic energy.

Awesome, that makes total sense. Thanks!
 

FAQ: Kinetic Energy Equation conceptual question?

1. What is kinetic energy?

Kinetic energy is the energy an object possesses due to its motion. It is a scalar quantity and is dependent on an object's mass and velocity.

2. What is the equation for kinetic energy?

The equation for kinetic energy is KE = 1/2 * m * v^2, where KE represents kinetic energy, m represents mass, and v represents velocity.

3. How does an object's mass affect its kinetic energy?

An object's mass directly affects its kinetic energy. As mass increases, the kinetic energy also increases, assuming the velocity remains constant.

4. How does an object's velocity affect its kinetic energy?

An object's velocity has a greater effect on its kinetic energy compared to its mass. As velocity increases, the kinetic energy increases at a faster rate, as it is squared in the kinetic energy equation.

5. Can an object have zero kinetic energy?

Yes, an object can have zero kinetic energy if it is at rest. Kinetic energy is only present when an object is in motion.

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