A 325-kg merry-go-round with a radius of 1.50 m is spinning counterclockwise, as viewed from above, at 4.80 rad/s. A 35.0-kg child is hanging on tightly 1.25 m from the rotation axis. Her father applies friction to the outer rim to slow the merry-go-round to a stop in 5 s. Model the merry-go-round as a solid disk, and define counterclockwise as the positive direction of rotation. How much torque t must the child's father apply? 432 N-m Incorrect

A 325-kg merry-go-round with a radius of 1.50 m is spinning counterclockwise, as viewed from above, at 4.80 rad/s. A 35.0-kg child is hanging on tightly 1.25 m from the rotation axis. Her father applies friction to the outer rim to slow the merry-go-round to a stop in 5 s. Model the merry-go-round as a solid disk, and define counterclockwise as the positive direction of rotation. How much torque t must the child's father apply? 432 N-m Incorrect

University Physics Volume 1

18th Edition

ISBN:9781938168277

Author:William Moebs, Samuel J. Ling, Jeff Sanny

Publisher:William Moebs, Samuel J. Ling, Jeff Sanny

Chapter10: Fixed-axis Rotation

Section: Chapter Questions

Problem 84P: You have a grindstone (a disk) that is 90.0 kg, has a 0.340-m radius, and is turning at 90.0 rpm,...

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Suppose a child walks from the outer edge of a rotating merry-go-round to the inside. Does the angular velocity of the merry-go-round increase, decrease, or remain the same? Explain your answer. Assume the merry-go-round is spinning without friction.
A 4.0-kg particle moves in a circle of radius 2.0 m. The angular momentum of the particle varies in time according to l=5.0t2 , (a) What is the torque on the particle about the center of the circle at t=3.4s ? (b) What is the angular velocity of the particle at t=3.4s ?
You have a grindstone (a disk) that is 90.0 kg, has a 0.340-m radius, and is turning at 90.0 rpm, and you press a steel axe against it with a radial force of 20.0 N. (a) Assuming the kinetic coefficient of friction between steel and stone is 0.20, calculate the angular acceleration of the grindstine. (b) How many turns will the stone make before coming to rest?
In 2015, in Warsaw, Poland, Olivia Oliver of Nova Scotia broke the world record for being the fastest spinner on ice skates. She achieved a record 342 rev/min, beating the existing Guinness World Record by 34 rotations. If an ice skater extends her aims at that rotation rate, what would be her new rotation rate? Assume she can be approximated by a 45-kg rod that is 1.7 m tall with a radius of 15 cm in the record spin. With her aims stretched take the approximation of a rod of length 130 cm with 10 of her body mass aligned perpendicular to the spin axis. Neglect frictional forces.
A bug of mass 0.020 kg is at rest on the edge of a solid cylindrical disk (M=0.10kg,R=0.10m) rotating in a horizontal plane around the vertical axis through its center. The disk is rotating at 10.0 rad/s. The bug crawls to the center of the disk. (a) What is the new angular velocity of the disk? (b) What is the change in the kinetic energy of the system? (c) If the bug crawls back to the outer edge of the disk, what is the angular velocity of the disk then? (d) What is the new kinetic energy of the system? (e) What is the cause of the increase and decrease of kinetic energy?
A baseball catcher extends his arm straight up to catch a fast ball with a speed of 40 m/s. The baseball is 0.145 kg and the catcher’s arm length is 0.5 m and mass 4.0 kg. (a) What is the angular velocity of the arm immediately after catching the ball as measured from the arm socket? (b) What is the torque applied if the catcher stops the rotation of his arm 0.3 s after catching the ball?
The centrifuge at NASA Ames Research Center has a radius of 8.8 m and can produce farces on its payload of 20 gs or 20 times the force of gravity on Earth. (a) What is the angular momentum of a 20-kg payload that experiences 10 gs in the centrifuge? (b) If the driver motor was turned off in (a) and the payload lost 10 kg, what would be its new spin rate, taking into account there are no frictional forces present?
The blades of a wind turbine are 30 m in length and rotate at a maximum rotation rate of 20 rev/min. (a) If the blades are 6000 kg each and the rotor assembly has three blades, calculate the angular momentum of the turbine at this rotation rate. (b) What Is the torque require to rotate the blades up to the maximum rotation rate in 5 minutes?
A diver off the high board imparts an initial rotation with his body fully extended before going into a tuck and executing three back somersaults before hitting the water. If his moment of inertia before the tuck is 16.9kgm2 and after the tuck during the somersaults is 4.2kgm2 , what rotation rate must he impart to his body directly off the board and before the tuck if he takes 1.4 s to execute the somersaults before hitting the water?
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