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# H-sol - Chapter H Problems Blinn College Physics 2425 Terry...

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Problem H.4 A car races around a circular track of radius 250 m at a constant speed of 45 m ê s . (a) What is its angular velocity? (b) What is the magnitude and direction of its acceleration? Solution to H.4 R = 250 m and v = 45 m H a L v = r w ï w = v R = 0.18 rad s H b L a c = w 2 r = v 2 R = 8.1 m s 2 The direction of the acceleration is centripetal, meaning that is directed toward the center. Problem H.5 By rotating through 1.25 rev of a 1 m radius arc, a discus thrower uniformly accelerates a discus from rest to 25 m ê s . (a) What is the final angular velocity of the discus? (b) What is its angular acceleration? (c) What is the total time of acceleration? Solution to H.5 H a L v = r w ï w = v r = 25 1 = 25 rad s H b L w 2 -w 0 2 = 2 a Dq ï 25 2 - 0 = 2 a H 2 1.25 L ï a = 39.8 rad s H c L Dq = 1 2 I w 0 + w M t ï 2 1.25 = 1 2 H 0 + 25 L t ï t = 0.628 s Problem H.6 Assume that a baseball is a uniform sphere of radius 3.80 cm. If it moves at a speed of 38 m ê s (the speed of the center of mass) and rotates at 125 rad ê s then what is the ratio of the rotational kinetic energy to the translational kinetic energy. Solution to H.6 For a uniform solid sphere I = 2 5 M R 2 K rot = 1 2 I w 2 = 1 2 2 5 M R 2 w 2 = 1 5 M R 2 w 2 K rot K trans = 1 5 M R 2 w 2 1 2 M v 2 = 2 R 2 w 2 5 v 2 2 Chapter H - Problems
Insert the numbers: R = 0.038 m , v = 38 m s and w = 125 rad s giving K rot K trans = 0.00625 . Problem H.7 Three masses glued onto a light rigid sheet in the xy plane. The masses and positions are: 4 kg at H - 3 m, 5 m L , 6 kg at H 4 m, 0 L and 8 kg at H 0, - 3 m L . (a) Suppose this sheet is rotated about the y axis at an angular velocity of 12 rad ê s. What is its total rotational kinetic energy? (b) Suppose it rotates about the z axis at 12 rad/s. What is its rotational kinetic energy?

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H-sol - Chapter H Problems Blinn College Physics 2425 Terry...

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