Alight source whose surface is approximated by a circle with a radius of 3 cm is located 2 m from a screen. if an aperture with a 1-cm radius is placed between the source and the screen, how far from the screen can the aperture be placed without affecting the irradiance in the screen at the center of the patch of light passed by the aperture? if the aperture is moved twice as far from the screen, what will be the irradiance at the center of the patch as a fraction of the unobstructed irradiance?

The of a machine determines its "usefulness." a. input force b. output force c. mechanical advantage

1point) a skydiver weighing 130 lb (including equipment) falls vertically downward from an altitude of 14,000 ft and opens the parachute after 20 s of free fall. assume that the force of air resistance, which is directed opposite to the velocity, is of magnitude 0.85|v|0.85|v| when the parachute is closed and is of magnitude 17|v|17|v| when the parachute is open, where the velocity vv is measured in ft/s. assume that acceleration due to gravity has magnitude 32 ft/s/s; remember that weight is the product of mass and gravitational acceleration. find the speed of the skydiver when the parachute opens. speed is 150.6121788 ft/s find the skydiver's height when the parachute opens. height is 2338.98591 ft find the limiting velocity vlvl after the parachute opens. (think about whether this should be positive or negative.) vl=vl= 7.647 ft/s

Agas expands from an initial volume of 0.040 m^3 and an initial pressure of 210 kpa to a final volume of 0.065 m^3 while its temperature is kept constant. how much work is done by the system?