Is the work-kinetic energy theorem violated?

Question

You are shelving books in a library. You lift a book from the floor to the top shelf. The KE of the book on the floor was 0, & the KE of the book on the top shelf is 0, so there is no change in KE. Yet you did some work in lifting the book. Is the work-Kinetic energy theorem violated?

& LAST question (some assistance please)

- A ball is throw straight up into the air. At what position is the KE a maximum? At what position is the gravitiational potential energy a maximum?

Answer 1

Oh, but there is a definite change in potential energy on that book - as a result of your work, the book has gained potential energy, which may well be converted to kinetic energy if it falls off the shelf.
The kinetic energy (velocity) is maximum the instant before it hits the ground - the potential energy is maximum at the highest point of its travel.

Answer 2

1

Answer 3

The paintings performed on an merchandise is the same because the replace contained in the article's kinetic ability. contained with reference to the falling merchandise, the paintings performed is the rigidity of gravity situations the gap the article has fallen, or 2 kg * 9.80 one m/s^2 * 12 m, for a finished of 235.40 4 J. This paintings will strengthen the article's kinetic ability with the aid of 235.40 4 J. because the article change into initially table sure before being dropped (kinetic ability change into 0), the entire kinetic ability of the article must be 235.40 4 J Plug that into the kinetic ability equation (KE = a million/2 m * v^2) and sparkling up for v: 235.40 4 J = a million/2 * 2 kg * v^2 v^2 = 235.40 4 m^2/s^2 v = 15.3 m/s

Answer 4

When the book was on the floor, its K.E was zero.

When you lifted the book from the floor to the top, you were very careful enough that the book gained no K.E. (Net force acting on the book was zero).

Thus it has gained no speed.
Through out its path from floor to top its speed is zero.

Then the question arises without any speed however small, how the book can move from the floor to the top.

The situation has to be understood as follows.

From the floor to a very small distance up or for a small interval of time, the book gains a small speed. That is, it has gained a very small K.E. After that it moves with constant speed till it reaches very near to the final point. Thereafter we make it to be at rest at that point. It implies, we have removed the kinetic energy that we imparted to it at the beginning of motion.

Thus there is no net gain of K.E by the book.

We can also think in a different way. The whole path can be split up into a number of bits of very small distances. And, the above story can be applied to each bit of distances. In each bit of distances we are removing the kinetic energy.

Another way of thinking is: the object gains a very small speed so that moving through a very small distance, its speed becomes zero. Again the object is given a very small speed at that point and then comes to rest. The process is repeated till the object comes to the final stage.

In all the cases the net gain of kinetic energy is zero.


For the second part of question, at the start its P.E is zero. But we have given some K.E to the object. As it goes up its speed decreases and when the speed is zero its K.E is zero. It is obvious that the K.E is the maximum at the initial stage.

When the object returns to the ground it regains its K.E which it has lost during its upward journey.

Answer 5

Don't know what you mean by the work-Kinetic energy theorem.

But what happens is the work I did is stored as potential energy m*g*h.

&
KE is a maximum as it leaves the hand (or when it returns to the ground). Max velocity.
The gravitiational potential energy is a maximum at the top of its path where velocity goes to zero.