wen is the poental energy equal to the kinetic eneergy.......?

Answer 1

Throw a ball straight up in the air. When it's half way up to its highest point potential energy and kinetic energy will be equal.

Answer 2

What I think you are looking for is when is potential energy converted to an equal magnitude of kinetic energy.

The simple answer to that is: whenever the object with the potential energy is put into motion without losses in energy.

Potential energy (PE) simply means an object with PE has a potential for doing work given the right circumstances. For example, if we raise a block of weight W = mg = 1 pound h = 2 feet into the air above ground, we put J = Wh = 1*2 = 2 ft-pounds of work into raising that block. So that block has the potential (PE = J = Wh) for doing 2 ft-lbs of work if given the chance.

Now I drop the block. As it falls, it loses potential energy because the height h is getting smaller. The law of conservation of energy says energy can be neither created nor destoryed. So that lost PE has to be going somewhere. And that somewhere is kinetic energy (KE). As the block falls, it accelerates due to gravity; so its velocity increases unitl it hits the ground level.

Kinetic energy is KE = 1/2 mv^2; where m is the mass of the object and v is its current velocity. (Note...before the block is released, v = 0; so it has no KE before the block is dropped.) Thus we have, from the conservation of energy, E = PE + KE = constant; where E is the total energy of the system (the block in this case). As you can see, if PE gets smaller, KE has to get bigger to keep the overall energy level E constant.

Finally, when the block hits ground level, which is h below the point where the block was released, we have E = PE + KE = KE because PE = mgh = 0 as h = 0 when the block strikes the ground level. Thus all the energy in that block has been converted to kinetic energy just as it impacts the ground. So we can, and frequently do, write that all the PE lost = all the KE gained during the fall. Thus PE = KE for short.

But, and this is a big BUT, PE = KE if and only if there are no energy losses. For example, if we had a weightless parachute attached to the block and the chute deployed upon dropping the block, there would be drag forces acting against the fall to slow the fall down. That is, after all, the purpose of a parachute...to slow down the fall velocity.

Thus the kinetic energy with the chute ke < KE without the chute. That results because 1/2 mv^2 < 1/2 mV^2; where the chute velocity v < V the velocity without the chute. In this case we have E = PE + ke + (Dh) = constant; where Dh is the lost energy due to drag forces (D) from the chute. The overall energy is still E, a constant, but now the chute drag energy saps some of the kinetic energy that would otherwise result.

So there you are...potential energy is equal to kinetic energy when there are no energy losses like drag energy. So if there are no losses, we can write PE = KE. But if there are losses, we must write PE = ke + lost energy and PE <> ke.

Answer 3

Can't answer that question without more information.

Potential energy is energy due to position or orientation (for example, due to height within a gravitational field); so its amount is relative to some position which you arbitrarily call "zero."

If you're talking about the case where you toss something straight up into the air, the "zero" point is usually (but not always) chosen to be ground level. If you're talking about something like a swinging pendulum, the "zero" point is usually chosen to be at the bottom of the swing. If you're talking about potiential/kinetic energy in an oscillating spring, the "zero" point is often chosen to be the point where the spring is neither stretched nor compressed.

Then, once you've chosen the zero point, the question of when the PE is equal to the KE, depends on the problem. The answer is different for all three of the examples I gave above; and there are many other examples I didn't mention.

So--give some more information!

Answer 4

The sum of the potential energy and kinetic energy is the total energy,

By law of conservation of energy, if we assume that there is no other energy involved, and then sum of the K.E and P.E remains the same.

From this it follows that change in kinetic energy equals change in potential energy.

The kinetic energy of a body is zero if its speed is zero; where as the potential energy depends on the position of the body. The position is arbitrary. That is it depends upon the reference frame in which we measure the position with respect to the origin of the frame of reference.

Hence in one and the same position we can make a body to have Kinetic energy equal to the potential energy by changing its speed or for a given speed, we can define the potential energy such that it is equal to kinetic energy.

Thus at any time and at any place we can make K.E as equal to the P.E.
However the energies once defined the total energy will remain the same.

To understand the above let us define the potential energy on ground as zero. Then at a height h above ground its potential energy of a mass is mgh.

Now consider a huge plate form at that height and the mass is moving with a speed v on that platform such that mgh = 1/2 mv^2. The P.E = K.E

The total energy is mgh + 1/2 mv^2.
But since there is a platform all of us can go there and now for us it is the ground.

The potential energy is now zero; whereas the kinetic energy is 1/2 mv^2.

In order to make P.E = K.E we will stop the object's motion.

Thus at our will we can make P.E = K.E

The answer to your question is at any time at any place we can make P.E = K.E.

Answer 5

PE and KE can be equal when velocity and height are both equal to 0. In that case, PE and KE are equal to 0.

Also when v^2 = 2gh, then PE and KE are both equal.
(You can put KE = PE, which means mv^2 = 2mgh to derive the equation)

Hope this helps.

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Answer 6

When object falls from top a building, has you let go of the object.. the P.E transfers to K.E therefore P.E = K.E