5-2

a)
$F=55N-6{,}5N=48{,}5N$
$a=\frac{48{,}5N}{5{,}6kg}=8{,}66...\ \frac{m}{s^2}$
b)
$\Sigma\overline{F}=\overline{G}+\overline{N}$

$\Sigma F=G-N=55N-55N=0N$

$m=5{,}6kg$

$\Sigma F=ma$
$a=\frac{\Sigma F}{m}=\frac{0N}{5{,}6kg}=0\frac{m}{s^2}$