The following apparatus can be used to measure atomic and molecular speed. Suppose that a beam of metal atoms is directed at a rotating cylinder in a vacuum. A small opening in the cylinder allows the atoms to strike a target area. Because the cylinder is rotating, atoms traveling at different speeds will strike the target at different positions. In time, a layer of the metal will deposit on the target area, and the variation in its thickness is found to correspond to Maxwell's speed distribution. In one experiment it is found that at 850°C some bismuth (Bi) atoms struck the target at a point 2.80 cm from the spot directly opposite the slit. The diameter of the cylinder is 15.0 cm and it is rotating at 130 revolutions per second.
(a) Calculate the speed (m/s) at which the target is moving. (The circumference of a circle is given by 2pr, where r is the radius.)
(b) Calculate the time (in seconds) it takes for the target to travel 2.80 cm.
(c) Determine the speed of the Bi atoms. Compare your result in (c) with the urms of Bi at 850°C. Comment on the difference.

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Rotating cvlinder Target Bi atoms Slit