1. You lift a block of concrete (mass 15kg) a vertical distance of 0.5 meter abo
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Question
1. You lift a block of concrete (mass 15kg) a vertical distance of 0.5 meter above the floor. You do not have any help from levers, pulleys, other machines or persons. a. Is external work done on the concrete mass? How much work? (Show work, show units) b. Is your muscle contraction isometric or isotonic, or both? Explain. c. Is internal work done by the muscle? d. Identify two internal structures within the muscle that change their length when the concrete block is lifted? Explain what happens to them (do they shorten or lengthen, and why?)Explanation / Answer
1.(a) The external work done on the concrete mass is given as:
W=(F)(d)
W=(m)(g)(d)
Where W is work done , F is force applied, d is displacement, g is acceleration due to gravity on the concrete mass.
W= 15kg(9.8m/s2)(0.5m)
W=73.5kgm2/s2
Or W= 73.5 joules.
(b) when a muscle is activated and required to lift a load which is less than the maximum tetanic tension it can generate, the muscles begin to shorten. Contractions that permit the muscles to shorten are reffered to as concentric contractions, a type of isotonic contractions.
(c) If a part of body system exerts a force on the another part of the same system,the workdone is called internal work. In case of lifting a block, internal work is also done by the muscles.
(d) when the block is lifted sarcomere contracts,myosin heads attach to actin to form cross- bridges. Then the thin filament slides over the thick filament as the heads pull the actin. This results in sarcomere shortening created tension of muscle contraction.
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