Parallel laser beam (=550 nm) falls perpendicularly on the opaque screen that has a circular opening with diameter D=2 mm. A dark spot is observed at a distance b1=18 cm on the central axis behind the screen. What is the minimal distance b that one has to move away from this spot and further away from the screen in order to observe a dark spot again?

Astone is dropped from the upper observation deck of a tower, 250 m above the ground. (assume g = 9.8 m/s2.) (a) find the distance (in meters) of the stone above ground level at time t. h(t) = (b) how long does it take the stone to reach the ground? (round your answer to two decimal places.) s (c) with what velocity does it strike the ground? (round your answer to one decimal place.) m/s (d) if the stone is thrown downward with a speed of 2 m/s, how long does it take to reach the ground? (round your answer to two decimal places.) s