- #1

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Is it possible to use KE + PE = KE + PE

1/2mv^2 + mgh = 1/2mv^2 + mgh

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- Thread starter smbascug
- Start date

- #1

- 8

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Is it possible to use KE + PE = KE + PE

1/2mv^2 + mgh = 1/2mv^2 + mgh

- #2

Doc Al

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- #3

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How can you tell if energy is coserved or not?

- #4

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smbascug said:How can you tell if energy is coserved or not?

Work is done, both by the puller and the frictional force. The friction generates heat, which certainly tells us that energy is not conserved.

- #5

Doc Al

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Mechanical energy is conserved if the only forces acting are conservative forces, like gravity. As Captain Zapp0 points out, here we have additional forces acting: the applied force and the friction. These forces do work on the object, changing its kinetic energy.smbascug said:How can you tell if energy is coserved or not?

If you attempted to use the conservation equation you quoted, you'll quickly find that it gets you nowhere since the gravitational PE doesn't change. (We assume that the crate is moving across a horizontal floor.)

- #6

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F= 100.0 N

d1==10.0m

KE(final) - KE(initial)

1/2mv^2 - 1/2mv^2

umm... how do i isolate v? or is this even correct?

- #7

Doc Al

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Find the work done by the forces during the first 10m and the second 10m. The total work done will equal the change in the crate's KE.

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