Lab Homework: Rotational Motion 2. In lab you released a mass tied to a string that was wrapped around a disc, and took a picture of the blinkie as the mass fell and the disc rotated. Suppose that instead you had unwound the string until the mass was just above the floor, and then someone in your group had pulled quickly down on the edge of the disc as shown. If you took a picture of the blinkie after the quick pull but while the mass rose was still rising, what would the picture look like? Explain. 3. What is the angular velocity of the earth as it spins on its axis? Express your answer in radians per second. Show how you determined your answer. 4. A blinkie photograph made using the same procedure as in section 4 of the lab is shown at right. The blinkie is flashing five times per second. 269 i. What is the duration of a single on/off cycle for the blinkie? 38 150 ii. What is the approximate angular velocity (in radians per second) of 62 the blinkie at point P? Show how you determined your answer. iii. If the speed of the blinkie at point P was 32 cm/sec, what is the distance from the center of the disc to the blinkie? Show how you determined your answer. iv. What is the approximate angular acceleration of the blinkie (in radians per second squared) of the blinkie at point P? Show how you determined your answer? Copyright 2008 by S. Kanim, M.Loverude, & L.Gomez 2Name Section Homework: Rotational Motion 1. Three children, Aricelia, Bao, and Chuck, are playing on a merry-go-round. Their positions on the merry-go-round are shown in the top-view picture at right. The merry-go- round is rotating clockwise and is neither speeding up nor slowing down. The Bad A. Rank the speeds of the children. If all of the children Aricelia are moving at the same speed, state that explicitly. Explain your reasoning. Chuck B. Rank the angular velocities of the children. If all of the children have the same angular velocity, state that explicitly. Explain your reasoning. C. Rank the times that it takes each child to complete one revolution. If all of the times are the same, state that explicitly. Explain your reasoning. D. With Aricelia, Bao, and Chuck on the merry-go-round, a fourth child, David, wants to bring the merry-go-round from rest to a rotation rate of 1 revolution every 4 seconds in as little time as possible. as possible. That is, he wants to be able to speed the merry-go-round up from rest as quickly Does it matter where the other three children sit on the merry-go-round? If you were David, inertia. where would you ask the other three children to sit? Explain based on the idea of moment of Copyright 2008 by S. Kanim, M.Loverude, & L.Gomez