A student sits on a freely rotating stool holding two dumbbells, each of mass 3.09 kg (see figure below). When his arms are extended horizontally (Figure a), the dumbbells are 0.97 m from the axis of rotation and the student rotates with an angular speed of 0.759 rad/s. The moment of inertia of the student plus stool is 2.77 kg m and is assumed to be constant. The student pulls the dumbbells inward horizontally to a position 0.309 m from the rotation axis (Figure b). Wi wf (a) Find the new angular speed of the student. rad/s (b) Find the kinetic energy of the rotating system before and after he pulls the dumbbells inward. Kbefore = Kafter = ] J An object of mass m = 0.530 kg is suspended from the ceiling of an accelerating truck as in the figure below. Take a = 3.20 m/s. a (a) Find the angle (in degrees) that the string makes with the vertical. 17 The object is accelerating at the same rate as the truck, so there must be a net force acting on the object. What is responsible for this net force? (b) Find the tension 7 (in N) in the string. 5.183 The tension is not equal to mg. If you consider the vertical components of the forces you will see why this is so. N What If? The truck returns to a constant velocity so that the mass hangs straight down inside the truck, whereby 0 = 0. Later, the truck carefully slows down. During this braking maneuver, the string is observed to make a constant angle of =23.0 with the vertical. (c) What is the acceleration of the truck (in m/s) while it is braking? m/s (d) What is the direction of the deflection of the string while the truck is braking? O forward backward