Okay i'm totally stuck and nobody i know really gets it either, so i've turned to yahoo for : )
basically there are four aliens on a planet. they want to go on a sea-saw. the end seats on the sea-saw are 2m from the pivot, and the middle seats are 1m from the pivot. the aliens way 400n, 300n, 200n and 100n - which two can sit on the sea-saw (on any of the seats) and make it balance? it'd be a huge if you at least me work out the answer! : )

The pressure increases by 1.0 x 104 n/m^2 for every meter of depth beneath the surface of the ocean. at what depth does the volume of a pyrex (bulk modulus 2.6 x 1010n/m^2) glass cube, 9.8 x 10^−2m on an edge at the ocean's surface, decrease by 7.5 x 10−10m^3? explain the formula beyond this point: p=1.0x10^4, b=2.6x10^10, l=9.8x10^−2, delta v=7.5x10^−10. at some point l needs to be cubed. why p is divided by delta v?

As you are trying to move a heavy box of mass m, you realize that it is too heavy for you to lift by yourself. there is no one around to , so you attach an ideal pulley to the box and a massless rope to the ceiling, which you wrap around the pulley. you pull up on the rope to lift the box. use g for the magnitude of the acceleration due to gravity and neglect friction forces. once you have pulled hard enough to start the box moving upward, what is the magnitude f of the upward force you must apply to the rope to start raising the box with constant velocity? express the magnitude of the force in terms of m, the mass of the box.

The dot diagram represents the motion of the motorcycle as it moves from left to right