Mercury's surface has many craters because .

it has no atmosphere to protect it from meteoroids or comets
it has several active volcanoes which erupt and melt holes in the rock
it once collided with another planet, which caused damage to its crust
it has a thick atmosphere which traps meteoroids and comets near the surface

Molten iron fills a mould, which has a volume of 200 cm cubed. calculate the volume when the iron cools and solidifies.

Global warming will produce rising sea levels partly due to melting ice caps but also due to the expansion of water as average ocean temperatures rise. to get some idea of the size of this effect, calculate the change in length of a column of water 1.00 km high for a temperature increase of 1.00ºc. note that this calculation is only approximate because ocean warming is not uniform with depth. (answer in ×10^{-3} −3 m)

As the distance from a magnet increases, what happens to the magnet force?