a. w = wđ + wt = mgz = 2.10.25 = 500 (J)

b. w = wA

<=> 500 = wđA + wtA

=> wđA = 500 J

=> vA = 10√5 m/s

c. w = wc

<=> 500 = wđC + wtC

<=> 500 = 1/2mvC^2 + mgzC

<=> 500 = 1/2.2.vC^2 + 2.10.20

=> vC = 10 m/s

Đáp án:

\(\begin{array}{l}
a.W = 500J\\
b.\\
{W_{d\max }} = 500J\\
{v_{\max }} = 10\sqrt 5 m/s\\
c.v = 10m/s
\end{array}\)

Giải thích các bước giải:

\(\begin{array}{l}
a.\\
W = {W_{t\max }} = mg{h_{\max }} = 2.10.25 = 500J\\
b.\\
{W_{d\max }} = W = 500J\\
\frac{1}{2}mv_{\max }^2 = 500\\
\frac{1}{2}.2.v_{\max }^2 = 500\\
 \Rightarrow {v_{\max }} = 10\sqrt 5 m/s\\
c.\\
h' = 25 - 5 = 20m\\
W' = mgh' + \frac{1}{2}mv{'^2}\\
W = W'\\
500 = 2.10.20 + \frac{1}{2}.2.v{'^2}\\
 \Rightarrow v = 10m/s
\end{array}\)