T Nation

Mind Boggler

OK here’s a conceptual physics question that I just can’t seem to wrap my head around, and am required to answer for part of my physics lab:

If I pull a block of wood using 1 joule of energy across a table for 1 m, where does this joule of energy go after the block reaches the end of the meter stick, and
b) where will the joule of energy be 15min later.

I know that the kinetic energy of me pulling this block of wood with that amount of energy is transformed into some other form of energy (potential?), but what kind, and what difference does the time make?

That force is dissipated as heat. There is no potential energy in this situation. You didn’t raise or lower the block, which would change potential energy. Friction between the floor and the block resists your action. We all know that friction creates heat.

Therefore, I believe the joule you used to move the block dissapated as heat energy. If you know the average speed of heat radiation, you should be able to calculate where it will be after a certain amount of time.

The energy went in to heat from the friction between the block and table.

it works like this, the initial nrg lies in the motion, not in the block per ce, 0.5MVV (mass X velocity squared) = kinetic nrg, notice how distance isnt included, now if the block stops after one meter that joule would be dissipated as friction (heat). in an ideal environment (frictionless) the block would just keep on truckin at whatever initial velocity was imparted on it, until an opposing force (friction) stops it. clear as mud? good

thanks people - that question was bugging the fu*k out of me, now I can sleep better.

If you assume that the block is initally at rest, then you have to overcome the static friction, which will be greater than sliding friction. So once the block moves, it would accelerate (assuming a constant force were applied). So the energy would go into producing heat and momentum.

If the block were already moving, then it could be assumed to be in a state of equilibrium (though moving) and the energy would go only into producing heat.