contestada

A tree limb of mass 12 kg falls straight down. If air resistance exerts 27 N of force on the limb as it falls, what is the net force on the tree limb?
A. 118 N down
B. 27 N down
C. 15 N down
D. 91 N down

Respuesta :

Donek
[tex]Given:\\m=12kg\\g=9.81 \frac{m}{s^2} \\|\overrightarrow{F_a}|=27N\\\\Find:\\|\overrightarrow{F_n}|=?\\\\Solution:\\\\\overrightarrow{F_n}=\overrightarrow{F_a}+\overrightarrow{F_c}\\\\|\overrightarrow{F_c}|=mg\\\\\overrightarrow{F_a}\uparrow\;\;\;\land\;\;\;\overrightarrow{F_c}\downarrow\;\;\;\Rightarrow |\overrightarrow{F_n}|=|\overrightarrow{F_a}|-|\overrightarrow{F_c}|\\\\ |\overrightarrow{F_n}|=|\overrightarrow{F_a}|-mg\\\\|\overrightarrow{F_a}|=27N-12kg\cdot 9.81 \frac{m}{s^2}\approx -91N\\\\|\overrightarrow{F_n}|<0\Rightarrow \overrightarrow{F_n}\downarrow \\\\Correct\; is \;answer \;D[/tex]

91 N down is correct

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