Physics 163

Unit 5: Work, Energy and Power

Problem Set C

Problem 4:

A 231-gram baseball leaves the bat with a speed of 76.2 m/s. It sails through the air, encountering air resistance which does a total of -236 Joules of work on the ball over the course of its entire trajectory. What is its speed (in m/s) of the ball the instant prior to being caught (at the same height as which it was hit)?

• 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.