Work and Energy Legacy Problem #3 Guided Solution
Problem*
Lamar Gant, U.S. powerlifting star, became the first man to deadlift five times his own body weight in 1985. Deadlifting involves raising a loaded barbell from the floor to a position above the head with outstretched arms. Determine the work done by Lamar in deadlifting 300 kg to a height of 0.90 m above the ground.
Audio Guided Solution
When a force is applied to an object to cause that object to move we see that work is being done upon the object. Here in this problem we have Lamarck dead lifting a weight above his head. The mass that he is lifting is 300 kilograms and to lift it above his head he has to apply a force which is equivalent to the force of gravity. He is lifting at a distance of 1.9 meters. So to calculate the amount of work done upon the barbell we have to go the force times the distance times the angle between the force and the direction the object moves which is also up. We have to go Fd times the cosine of zero degrees. Now in this problem the force that is exerted upon the barbell is 300 kilograms times 9.8 or 2,940 newtons. We take the 2,940 newtons multiply it by 1.9 and then by the cosine of zero degrees. When we are done we have 5,586 joules of work being done. We can round this to two significant digits such that the answer becomes 5.6 x 10 to the third joules.
Solution
2.6 x 103 J
Habbits of an Effective Problem Solver
- Read the problem carefully and develop a mental picture of the physical situation. If necessary, sketch a simple diagram of the physical situation to help you visualize it.
- Identify the known and unknown quantities in an organized manner. Equate given values to the symbols used to represent the corresponding quantity - e.g., \(\descriptive{v}{v,velocity}_\descriptive{o}{o,original} = 0 \unit{\meter\per\second}\); \(\descriptive{a}{a,acceleration} = 4.2\unit{\meter\per\square\second}\); \(\descriptive{v}{v,velocity}_\descriptive{f}{f,final} = 22.9 \unit{\meter\per\second}\); \(\descriptive{d}{d,distance} = \colorbox{gray}{Unknown}\).
- Use physics formulas and conceptual reasoning to plot a strategy for solving for the unknown quantity.
- Identify the appropriate formula(s) to use.
- Perform substitutions and algebraic manipulations in order to solve for the unknown quantity.
Read About It!
Get more information on the topic of Work and Energy at The Physics Classroom Tutorial.