Listed following are three possible models for the long-term expansion (and possible contraction) of the universe in the absence of dark energy. rank each model from left to right based on the ratio of its actual mass density to the critical density, from smallest ratio (mass density much smaller than critical density) to largest ratio (mass density much greater than critical density).
1. coasting universe
2. recollapsing universe
3. critical universe

An airplane flies eastward and always accelerates at a constant rate. at one position along its path it has a velocity of 34.3 m/s, it then flies a further distance of 40100 m and afterwards its velocity is 47.5 m/s. find the airplane\'s acceleration and calculate how much time elapses while the airplane covers those 40100 m.

Which of the following are guidelines to follow for obtaining accurate observations

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?