Consider a sealed 20-cm-high electronic box whose base dimensions are 50 cm × 50 cm placed in a vacuum chamber. the emissivity of the outer surface of the box is 0.95. if the electronic components in the box dissipate a total of 120 w of power and the outer surface temperature of the box is not to exceed 55°c, determine the temperature at which the surrounding surfaces must be kept if this box is to be cooled by radiation alone. assume the heat transfer from the bottom surface of the box to the stand to be negligible.

As you are trying to move a heavy box of mass m, you realize that it is too heavy for you to lift by yourself. there is no one around to , so you attach an ideal pulley to the box and a massless rope to the ceiling, which you wrap around the pulley. you pull up on the rope to lift the box. use g for the magnitude of the acceleration due to gravity and neglect friction forces. once you have pulled hard enough to start the box moving upward, what is the magnitude f of the upward force you must apply to the rope to start raising the box with constant velocity? express the magnitude of the force in terms of m, the mass of the box.