4–15. the post is made of douglas fir and has a diameter of 100 mm. if it is subjected to the load of 20 kn and the soil provides a frictional resistance that is distributed along its length and varies linearly from w = 4 kn> m at y = 0 to w = 12 kn> m at y = 2 m, determine the force f at its bottom needed for equilibrium. also, what is the displacement of the top of the post a with respect to its bottom b? neglect the weight of the post.

If you were to drop a rock from a tall building, assuming that it had not yet hit the ground, and neglecting air resistance. what is its vertical displacement (in m) after 6 s?

Janelle made a hypothesis bout the uneven temperatures inside her house during winter. she believes that 50% of the ducts are blocked and she plans to investigate. if she wants to prove her hypothesis using scientific processes what should she do next?

The nuclear potential that binds protons and neutrons in the nucleus of an atom is often approximated by a square well. imagine a proton conned in an innite square well of length 105 nm, a typical nuclear diameter. calculate the wavelength and energy associated with the photon that is emitted when the proton undergoes a transition from the rst excited state (n 2) to the ground state (n 1). in what region of the electromagnetic spectrum does this wavelength belong?