Recent content by Prosthetic Head

The work done on the system by gravity is W = -ΔU, whether you are moving the stone up or down a gravitational potential, you just get either a positive or negative answer. When you were performing the calculation of the work you should have noted that F.x is the kinetic energy, thus: F(xf-xi)...

When considering work, you must be careful whether you are talking about the work done on the system or the work done by the system. Both these meanings are subject to how you wish to define work, both are equally valid but you must stick to the same one. Your first statement describes the...

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not necessarily, do you have any equations with which to calculate this?

oops that didnt work, I mean: F = F mg = GMm/[r][/2]

equating: F = F LaTeX Code: mg = G\\frac{Mm}{r^2}

those are the force equations!

looks good to me!

after equating the two force equations you should have been left with: g=G*M/r^2 you need to rearrange this for r and solve it

If half the volume of the block was below the boundary (5cm below) the block would have a density half way between that of oil and water (i.e 0.8 g/cm^3). From the density you could easily calculate the mass, try using the same argument for the numbers in your question.

Imagine the radiation leaving the sun as the surface of an expanding sphere, calculate the surface area of this sphere when it reaches the Earth's surface (i.e a sphere with a radius equal to the distance between the sun and the earth). By considering what proportion of the total surface area...

That is the correct answer, if you still don't understand try posting your workings and I'll show you where you have gone wrong.

This is just a thought that might simplify things a lot, the frequency of the wave describes how many times the wave passes a point per second, in this case an antinode. Also, each time the wave passes an antinode it has completed one full cycle from peak to trough and back to peak again.

Thats not right, and you still haven't expressed it in units of Earth radii.

Got confused there, thought Stratosphere had asked the question originally. ViralRiver already gave the relevant equation (s=d/t) you ( or ViralRiver really) need to rearrange that for t.