tbr physics section 3, question 49. Kinetic or chemical energy

[ibeatupnerds]

Ok, so a person lifts a block from the ground to a platform above the ground. I am thinking Kinetic energy changes to potential energy. easy.

but according to the book the right answer is: chemical potential energy is converted to potential chemical energy.

the explanation in the book is: The block starts and ends at rest, so kinetic energy is not part of the initial or final condition. To lift the block, the woman must convert some of her chemical potential energy to gravitational potential energy of the block.

Doesn't make any sense to me. I thought chemical potential energy was like rubber in a ball or a atom that bursts into alpha/beta particles.

So (I am making this up), if a block is on a ramp, than the person lets go of the block and it slides down the ramp and slides some on the level ground (till friction stops it). Would saying "potential energy is converted to kinetic energy" wrong for this? since the block starts as rest and ends at rest too?

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[whiteshadodw]

Ok, so a person lifts a block from the ground to a platform above the ground. I am thinking Kinetic energy changes to potential energy. easy.

but according to the book the right answer is: chemical potential energy is converted to potential chemical energy.

the explanation in the book is: The block starts and ends at rest, so kinetic energy is not part of the initial or final condition. To lift the block, the woman must convert some of her chemical potential energy to gravitational potential energy of the block.

Doesn't make any sense to me. I thought chemical potential energy was like rubber in a ball or a atom that bursts into alpha/beta particles.

So (I am making this up), if a block is on a ramp, than the person lets go of the block and it slides down the ramp and slides some on the level ground (till friction stops it). Would saying "potential energy is converted to kinetic energy" wrong for this? since the block starts as rest and ends at rest too?

or chemical potential energy of glucose/sugar/fats/whatever in your body get oxidized to release energy to perform mechanical work in lifting the box from a lower height to a higher height.

 

[MD Odyssey]

Consider the energies of the various parts of the system prior to the event. The box is on the ground, so U = mgh = 0. There is nothing moving, so we conclude that kinetic energy is also equal to zero. If there were energy at all, nothing could be done, so clearly there is another source. That leads us to examine the woman. There are only a few kinds of potential energies that you've learned about: gravitational, Hooke's law, and electrostatic.

Recall how muscle fibers are made to contract by the interaction of actin and myosin. It requires the hydrolysis of ATP, right? The bond between ADP and phosphate is a very high energy bond and has the potential to be used for something - it is chemical energy which the woman puts to use when she lifts the box from the ground up to the platform.

After the event is over, the woman has used that chemical energy derived from ATP to change the potential energy of the box, or in other words, has done some work on the box.

An interesting question to ask is this: Did all the chemical energy stored in her muscles get converted into potential energy? Nope. Some of it was lost to the environment, which is why, if she were to lift boxes all day, she would get hotter.

Hope this helps.