Physics 163

Unit 5: Work, Energy and Power

Problem Set C

Problem 10:

A 843-kg roller coaster car is lifted to a height of 57.1 meters above the ground where it begins its descent from an initial rest position. A total of -14061 Joules of work are done on the car by air resistance as it descends the first hill and rises to the top of the first loop - a height of 16.2 m. What is its speed (in m/s) at the top of this loop?

• 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.

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