Infinite square lattice, and 5. A sailor is in a sailboat on a river. The current is 3 knots with respect to the land. The sailor wants to proceed downriver as quickly as possible, maximizing his downstream speed with respect to the land. Assume that the Sun is stationary and that the Earth's orbit around it is circular.
Solution spheres Two spheres are the same size and weight, but one is hollow.
They are each made of uniform material, though of course not the same material.