8.In which of the following scenarios is work being done, according to the physics definition?a. Joe solves a “work” calculation in his head.b. Shauna places her chair onto the desk after the afternoon announcements.c. Garrett holds a barbell over his head in weightlifting class.d. Paige carries a reference book across the classroom. Sgsgsgsg G. a. A weightlifter holds a barbell overhead for 2.5 s. b. A construction worker carries a heavy beam while walking at constant speed along a flat surface. c. A car decelerates while traveling on a flat stretch of road. d. A student holds a spring in a compressed position. 2 Answers By Expert Tutors (A) No work, no change in overall elevation of the weight. (B) If there is friction between the feet of the construction worker and the floor, the friction force creates negative work. Since friction opposes line of motion. (C) The friction force on the tires create negative work. In order for tires to move they need to have traction, traction is generated via the friction between the ground and the rubber tire. (D) There is work in the spring since we are compressing it. The only time we do not have work on a spring is when we hold the spring at natural unstretched state.
Frank A. answered • 10/27/20 Knowledge, experience and insight from decades of teaching physics.
Lets consider each of the scenarios in light of the definition of work. Work is said to be done if a net force acts on a body as the body displaces [in the direction of force]. Work = Fnet•dcosθ (as long as F and d are in exactly the same or opposite direction, cosθ=1) a. A weightlifter holds a barbell overhead for 2.5 s. As long as there is force but no displacement, work = 0 b. A construction worker carries a heavy beam while walking at constant speed along a flat surface. While the weight of the beam and friction are forces, they are balanced by other forces (constant velocity) so there is no net force even though there is displacement so W=0 c. A car decelerates while traveling on a flat stretch of road. Deceleration only occurs when there is net force and when objects are decelerating, there is displacement. Some work is done in this case. d. A student holds a spring in a compressed position. Once again there are forces but no displacement so no work is done. W=0 Mr. A Recommended textbooks for you College Physics Author:Raymond A. Serway, Chris Vuille Publisher:Cengage Learning University Physics (14th Edition) Author:Hugh D. Young, Roger A. Freedman Introduction To Quantum Mechanics Author:Griffiths, David J., Schroeter, Darrell F. Publisher:Cambridge University Press Physics for Scientists and Engineers Author:Raymond A. Serway, John W. Jewett Publisher:Cengage Learning Lecture- Tutorials for Introductory Astronomy Author:Edward E. Prather, Tim P. Slater, Jeff P. Adams, Gina Brissenden College Physics: A Strategic Approach (4th Editio... Author:Randall D. Knight (Professor Emeritus), Brian Jones, Stuart Field College Physics ISBN:9781305952300 Author:Raymond A. Serway, Chris Vuille Publisher:Cengage Learning University Physics (14th Edition) ISBN:9780133969290 Author:Hugh D. Young, Roger A. Freedman Publisher:PEARSON Introduction To Quantum Mechanics ISBN:9781107189638 Author:Griffiths, David J., Schroeter, Darrell F. Publisher:Cambridge University Press Physics for Scientists and Engineers ISBN:9781337553278 Author:Raymond A. Serway, John W. Jewett Publisher:Cengage Learning Lecture- Tutorials for Introductory Astronomy ISBN:9780321820464 Author:Edward E. Prather, Tim P. Slater, Jeff P. Adams, Gina Brissenden Publisher:Addison-Wesley College Physics: A Strategic Approach (4th Editio... ISBN:9780134609034 Author:Randall D. Knight (Professor Emeritus), Brian Jones, Stuart Field Publisher:PEARSON |