Đáp án:
\(\begin{array}{l}
4.m = 60g\\
5.\\
a.v = 10\sqrt 5 m/s\\
bh = 12,5m
\end{array}\)
Giải thích các bước giải:
\(\begin{array}{l}
4.\\
W = mgh + \frac{1}{2}m{v^2}\\
1380 = m.10.300 + \frac{1}{2}.m{.200^2}\\
\Rightarrow m = 0,06kg = 60g\\
5.\\
a.\\
{W_{t\max }} = {W_{d\max }}\\
mg{h_{max}} = \frac{1}{2}m{v^2}\\
10.25 = \frac{1}{2}.{v^2}\\
\Rightarrow v = 10\sqrt 5 m/s\\
b.\\
{W_t} = {W_d} = \frac{{{W_{t\max }}}}{2}\\
mgh = \frac{{mg{h_{\max }}}}{2}\\
\Rightarrow h = \frac{{{h_{\max }}}}{2} = \frac{{25}}{2} = 12,5m
\end{array}\)
