Physics 163

Unit 5: Work, Energy and Power

Problem Set C

Problem 7:

Esteemed Chinese ski jumper, Li Ping Phar, leaves the jump ramp with an initial speed of 33.1 m/s and a height (relative to the bottom of the ski hill) of 56.2 meters. She encounters -7624 Joules of work due to air resistance during her flight through the air. Determine the speed (in m/s) of her 45.2-kg body the instant prior to striking the ground at the bottom of the hill.

• Read the problem carefully and diagram the physical situation (initial-final state diagram and/or work-energy bar chart)
• Identify known and unknown information in an organized manner (write on diagram)
• Take the time to plot out a strategy prior to beginning the solution (cancel terms in work-energy equation and perform conversions when necessary)
• Identify an appropriate formula to use
• Perform step-by-step algebraic manipulations

0.5 • m • vi2 + m • g • h i + F • d • cos = 0.5 • m • vf2 + m • g • h f

General information about work and energy problems is described on the Set C Overview page.

A detailed discussion of how to analyze physical situations using work-energy bar charts is provided online at The Physics Classroom.

A detailed description of the work-energy relationships for situation in which external forces are doing work is provided online at The Physics Classroom.