Concept explainers
A reasonable estimate of the moment of inertia of an ice skater spinning with her arms at her sides can be made by modeling most of her body as a uniform cylinder. Suppose the skater has a mass of 64 kg. One-eighth of that mass is in her arms, which are 60 cm long and 20 cm from the vertical axis about which she rotates. The rest of her mass is approximately in the form of a 20-cm-radius cylinder.
a. Estimate the skater’s moment of inertia to two significant figures.
b. If she were to hold her arms outward, rather than at her sides, would her moment of inertia increase, decrease, or remain unchanged? Explain.
Want to see the full answer?
Check out a sample textbook solutionChapter 7 Solutions
College Physics: A Strategic Approach (3rd Edition)
Additional Science Textbook Solutions
Biology: Life on Earth (11th Edition)
Microbiology with Diseases by Body System (5th Edition)
Introductory Chemistry (6th Edition)
Genetic Analysis: An Integrated Approach (3rd Edition)
Human Biology: Concepts and Current Issues (8th Edition)
Chemistry: Structure and Properties (2nd Edition)
- A compact disc rotates at 500 rev/min. If the diameter of the disc is 120 mm, (a) what is the tangential speed of a point at the edge of the disc? (b) At a point halfway to the center of the disc?arrow_forwardSuppose when Earth was created, it was not rotating. However, after the application of a uniform torque after 6 days, it was rotating at 1 rev/day. (a) What was the angular acceleration during the 6 days? (b) What torque was applied to Earth during this period? (c) What force tangent to Earth at its equator would produce this torque?arrow_forwardA wheel 1.0 m in diameter rotates with an angular acceleration of 4.0rad/s2 . (a) If the wheel’s initial angular velocity is 2.0 rad/s, what is its angular velocity after 10 s? (b) Through what angle does it rotate in the 10-s interval? (c) What are the tangential speed and acceleration of a point on the rim of the wheel at the end of the 10-s interval?arrow_forward
- A flywheel (l=50kgm2) starting from rest acquires an angular velocity of 200.0 rad/s while subject to a constant torque from a motor for 5 s. (a) What is the angular acceleration of the flywhell? (b) What is the magnitude of the torque?arrow_forwardDuring a 6.0-s time interval, a fly-wheel with a constant angular acceleration turns through 500 radians that acquire an angular velocity of 100 rad/s. (a) What is the angular velocity at the beginning of the 6.0 s? (b) What is the angular acceleration of the fly-wheel?arrow_forwardDuring a very quick stop, a car decelerates at 7.00 m/s2. (a) What is the angular acceleration of its 0.280-m-radius tires, assuming they do not slip on the pavement? (b) How many revolutions do the tires make before coming to rest, given their initial angular velocity is 95.0 rad/s? (c) How long does the car take to stop completely? (d) What distance does the car travel in this time? (e) What was the car's initial velocity? (f) Do the values obtained seem reasonable, considering that this stop happens very quickly?arrow_forward
- An ultracentrifuge accelerates from to 100,000 rpm in 2.00 min. (a) What is the average angular acceleration in rad/s2 ? (b) What is the tangential acceleration of a point 9.50 cm from the axis of rotation? (c) What is the centripetal acceleration in m/s2 and multiples of g of this point at full rpm? (d) What is the total distance travelled by a point 9.5 cm from the axis of totation of the ultracentrifuge?arrow_forwardThe angular position of a rod varies as 20.0t2radians from time t=0 . The rod has two beads on it as shown in the following figure, one at 10 cm from the ratation axis and the other at 20 cm from the rotation axis. (a) What is the instantaneous angular velocity of the rod at t=5s ? (b) What is the angular acceleration of the rod? (c) What are the tangential speeds of the beads at t=5s ? (d) What are the tangential acceleration of the beads at t=5s ? (e) What are the centripetal accelerations of the beads at t=5s ?arrow_forwardA circular disk of radius 10 cm has a contant angular acceleration of 1.0rad/s2 ; at t=0 its angular velocity is 2.0 rad/s. (a) Determine the disk’s angular velocity at t=5.0s (b) What is the angle it has rotated through during this time? (c) What is the tangential acceleration of a point on the disk at t=5.0s ?arrow_forward
- A centrifuge used for training astronauts rotating at 0.810 rad/s is spun up to 1.81 rad/s with an angular acceleration of 0.050 rad/s2. a. What is the magnitude of the angular displacement that the centrifuge rotates through during this increase in speed? b. If the initial and final speeds of the centrifuge were tripled and the angular acceleration remained at 0.050 rad/s2, what would be the factor by which the result in part (a) would change?arrow_forwardIntegrated Concepts An ultracentrifuge accelerates from rest to 100,000 rpm in 2.00 min. (a) What is its angular acceleration in rad/s2? (b) What is the tangential acceleration of a point 9.50 cm from the axis of rotation? (c) What is the radial acceleration in m/s2 and multiples of g of this point at full rpm?arrow_forwardOn takeoff, the propellers on a UAV (unmanned aerial vehicle) increase their angular velocity form rest at a rate of =(25.0t)rad/s for 3.0 s. (a) What is the instantaneous angular velocity of the propellers at t=2.0s ? (b) What is the angular acceleration?arrow_forward
- University Physics Volume 1PhysicsISBN:9781938168277Author:William Moebs, Samuel J. Ling, Jeff SannyPublisher:OpenStax - Rice UniversityPrinciples of Physics: A Calculus-Based TextPhysicsISBN:9781133104261Author:Raymond A. Serway, John W. JewettPublisher:Cengage LearningPhysics for Scientists and Engineers: Foundations...PhysicsISBN:9781133939146Author:Katz, Debora M.Publisher:Cengage Learning
- College PhysicsPhysicsISBN:9781938168000Author:Paul Peter Urone, Roger HinrichsPublisher:OpenStax CollegeGlencoe Physics: Principles and Problems, Student...PhysicsISBN:9780078807213Author:Paul W. ZitzewitzPublisher:Glencoe/McGraw-HillCollege PhysicsPhysicsISBN:9781305952300Author:Raymond A. Serway, Chris VuillePublisher:Cengage Learning