0 poines OSCOPliys1 4.7 Calculate the force a mother must exert to hold her 12.0
ID: 2037559 • Letter: 0
Question
0 poines OSCOPliys1 4.7 Calculate the force a mother must exert to hold her 12.0 kg child in an elevator under the following conditions a) The elevator accelerates upward at 0.850 m/s. Calculate the ratio of this force to the weight of the child. (b) The elevator moves upward at a constant speed. Calculate the ratio of this force to the weight of the child (c) The upward bound elevator decelerates at 2.30 m/s2 Calculate the ratio of this force to the weight of the child. (d) Show the free body diagram used (same for all parts). Do this on paper. Your instructor may ask yExplanation / Answer
Weight of the Child
W = mg = 12.0 kg x 9.81 m/s² = 117.7 N
(a) The elevator accelerates upward at 0.850 m/s².
F = m(g + a) = 12.0 kg x (9.81 m/s² + 0.850 m/s²) = 12.0 kg x 10.66 m/s² = 127.9 N
Calculate the ratio of this force to the weight of the child.
127.9/117.7 = 1.087
(b) The elevator moves upward at a constant speed.
At a constant speed, the only acceleration acting on the child is gravity, so the child's weight
will be no different.
F = m(g + 0) = mg = 12.0 kg x 9.81 m/s² = 117.7 N
Calculate the ratio of this force to the weight of the child.
117.7/117.7 = 1.0
(c) The upward bound elevator decelerates at 2.30 m/s².
F = m(g - a) = 12.0 kg x (9.81 m/s² - 2.30 m/s²) = 12.0 kg x 7.51 m/s² = 90.1 N
Calculate the ratio of this force to the weight of the child.
90.1/117.7 = 0.7655 ? 0.77
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