Đáp án:
Bài 1:
\(\begin{array}{l}
a)\\
{\rm{W}} = mg{h_0} + \dfrac{1}{2}m{v_0}^2 = 56J\\
b)\\
{\rm{W}} = mg{h_{{\rm{max}}}} \Rightarrow {h_{{\rm{max}}}} = 56m\\
c)\\
v = {v_0} - gt = 0m/s \Rightarrow {{\rm{W}}_d} = 0J\\
{{\rm{W}}_t} = {\rm{W = 56J}}\\
{\rm{d) }}\\
x = 36 + 20t - 5{t^2}\\
x = 0 \Rightarrow 5,34s
\end{array}\)