A 5-kg mass is lifted vertically through 4 m by a cord withtension 80 N. Find (a

Question

A 5-kg mass is lifted vertically through 4 m by a cord withtension 80 N. Find (a) the work done by the cord, (b) thework done by gravity, (c) the final kinetic energy, (d) the finalvelocity. I got this question wrong on the exam. Professor did notexplain to us how to get the answer. someone please help me. Idon't want to make the same mistake on the exam. A 5-kg mass is lifted vertically through 4 m by a cord withtension 80 N. Find (a) the work done by the cord, (b) thework done by gravity, (c) the final kinetic energy, (d) the finalvelocity. I got this question wrong on the exam. Professor did notexplain to us how to get the answer. someone please help me. Idon't want to make the same mistake on the exam.

Explanation / Answer

mass m = 5 kg distanmce S = 4 m tension T = 80 N (a). The work done by the cord W = T S= 320 J (b). work done by gravity W ' = -mg S = -196 J (c). Let the initial velocity be zero . Initil kinetic energy K = 0 Change in kinetic energy = net work done            K' - K = W + W '                  K ' = 124 J i.e.,final kinetic energy K ' = 124 J (d). we know  K ' = ( 1/ 2) m v ^ 2      ( 1/ 2) m v ^ 2 = 124 J final velocity   v = [ 2 * 124 / m ]                        = 7.042 m / s                              

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