Electrons are fired at a rectangular potential energy barrier, once every 221 ms. If the barrier is 2.55 nm thick and has a height that exceeds the energy of the incident electrons by exactly 637 meV, how long on average would you expect to wait for one electron to pass through the barrier

1400 kg car has a speed of 27 m/s. if it takes 7 s to stop the car, what is the impulse and the average force acting on the car?

Assume that a person skiing high in the mountains at an altitude of h = 15100 ft takes in the same volume of air with each breath as she does while walking at sea level. determine the ratio of the mass of oxygen inhaled for each breath at this high altitude compared to that at sea level. assume that the air composition (i.e. % of air that is oxygen) is the same at sea level as it is at 15100 ft.

The first law of thermodynamics states that heat added to a system is neither created nor destroyed but is as it changes into other forms of energy.