Mechanics: Work and Energy

Work and Energy: Audio Guided Solution

Extra Problem 8:

A 67.4-kg man jumps from a window 0.783 m above a sidewalk. What is the speed (in m/s) just before his feet strike the pavement?

 

 

Audio Guided Solution

 

Use the equations below to solve this problem. Cancel terms, substitute and solve.

KE_i + PE_i + W_nc = KE_f + PE_f

0.5•m•v_i² + m•g•h _i + 0.5•k•x_i² + F•d•cos Θ = 0.5•m•v_f² + m•g•h _f + 0.5•k•x_f²

 

Read About It!

Get more information on the topic of Work and Energy at The Physics Classroom Tutorial.

• Work
• Sample Work Calculations
• Power
• Resolving the Weight Vector on an Inclined Plane
• Potential Energy
• Kinetic Energy
• Mechanical Energy
• Situations Involving External Forces
• Situations Involving Energy Conservation

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Habits of an Effective Problem Solver

An effective problem solver by habit approaches a physics problem in a manner that reflects a collection of disciplined habits. An effective problem-solver...

• ...reads the problem carefully and develops a mental picture of the physical situation. If needed, they sketch a simple diagram of the physical situation to help visualize it.
• ...identifies the known and unknown quantities in an organized manner, often times recording them on the diagram iteself. They equate given values to the symbols used to represent the corresponding quantity (e.g., v_o = 0 m/s; a = 4.2 m/s/s; v_f = 22.9 m/s; d = ???).
• ...plots a strategy for solving for the unknown quantity; the strategy will typically center around the use of physics equations be heavily dependent upon an understaning of physics principles.
• ...identifies the appropriate formula(s) to use, often times writing them down. Where needed, they perform the needed conversion of quantities into the proper unit.
• ...performs substitutions and algebraic manipulations in order to solve for the unknown quantity.