Đáp án:
\(\begin{array}{l}
a.\\
{W_t} = 500J\\
{W_t}' = - 500J\\
b.\\
{W_d} = 500J\\
v = 10\sqrt 2 m/s\\
c.z = \frac{{20}}{3}m
\end{array}\)
Giải thích các bước giải:
\(\begin{array}{l}
a.\\
{W_t} = mgz = 5.10.10 = 500J\\
{W_t}' = mgz' = 5.10.( - 10) = - 500J\\
b.\\
W = {W_{t\max }} = mg{z_{\max }} = 5.10.20 = 1000J\\
{W_d} = W - {W_t} = 1000 - 500 = 500J\\
{W_d} = \frac{1}{2}m{v^2}\\
500 = \frac{1}{2}.5{v^2}\\
\Rightarrow v = 10\sqrt 2 m/s\\
c.\\
{W_d} = 2{W_t} \Rightarrow {W_t} = \frac{W}{3}\\
mgz = \frac{{1000}}{3}\\
5.10.z = \frac{{1000}}{3}\\
\Rightarrow z = \frac{{20}}{3}m
\end{array}\)
