Đáp án:
\(\begin{array}{l}
28.\\
a.\\
W = 5\\
b.\\
v = = 2\sqrt 5 m/s\\
c.\\
{A_{ms}} = 2,75\\
{F_{ms}} = 1,375N\\
29.\\
a.\\
{W_d} = 12,5\\
b.\\
l = 2,5m
\end{array}\)
Giải thích các bước giải:
\(\begin{array}{l}
28.\\
a.\\
W = {W_t} = mgh = mgAB.\sin 30 = 0,5.10.2.\sin 30 = 5\\
b.\\
W' = W = {W_d} = \frac{1}{2}m{v^2}\\
v = \sqrt {\frac{{2W}}{m}} = \sqrt {\frac{{2.5}}{{0,5}}} = 2\sqrt 5 m/s\\
c.\\
W' = {W_d}' = \frac{1}{2}mv{'^2} = \frac{1}{2}.0,{5.3^2} = 2,25\\
{A_{ms}} = W - W' = 5 - 2,25 = 2,75\\
{F_{ms}} = \frac{{{A_{ms}}}}{{AB}} = \frac{{2,75}}{2} = 1,375N\\
29.\\
a.\\
{W_d} = \frac{1}{2}mv_0^2 = \frac{1}{2}{.1.5^2} = 12,5\\
b.\\
{W_d} = {W_t} = mgh = mgl.\sin 30\\
12,5 = 1.10.l.\sin 30\\
l = 2,5m
\end{array}\)
