Calcule a taxa de transferência de calor por convecção natural entre uma secao de area de 20x20 m do telhado de um barracão e o ar ambiente, se a tempera da superfície do telhado for de 27°c, a temperatura do ar -3°c e o coeficiente medio de transferência de calor é igual 10w/m2.k

Aloaded platform of total mass 500 kg is supported by a dashpot and by a set of springs of effective stiffness 72 kn/m. it is observed that when the platform is depressed through a distance x = 12.5 cm below its equilibrium position and then released without any initial velocity; it reaches its equilibrium position in the shortest possible time without overshoot. find the position and velocity of the loaded platform 0.10 sec. after its release. if a further load of 400 kg is added to the platform, find, i) the frequency of damped vibrations, and i) the amplitude of vibration after 2 complete oscillations, given that the initial amplitude is 15 cm.