En cierta casa con energía solar, se almacena energía del sol en barriles llenos con agua. En lapso de cinco días nublados de invierno, se necesitaron 5,22GJ para mantener el interior de la casa a 22°C. Suponiendo que el agua de los barriles estuviera a 50°C. ¿Qué volumen de agua se necesitó? c= 4190 J/kg. K

Space-time metric ds2= -dt2+at2dx2+bt2dy2+ct2dz2 (a)how does the area of a rectangle with vertices at ( x=0, y=0, z=0 ), (1,0,0 ), ( 0,1,0 ) and (1,1,0 ) changes with time? (b) if a photon moving in the x direction starts from the origin at t=1, when does it reach x=l? (ds=0 for the trajectory of a photon.) (c) the proper time for a particle is defined by cd=ds. what is the proper time for a particle to move along the trajectory ( x(t)=t, y(t)=0, z(t)=0 ) from t=0 to 1 ? what is the condition on the parameter a so that the velocity of the particle never exceeds the speed of light ?

Idon’t quite understand this problem

What is the stall speed at sea level of an airplane that weights 10000 lbs., has a wing area of 300ft^2, and a maximum lift coefficient of 1.4? what is the stall speed if flaps that double cl,max are applied?