Đáp án:

a) \(960N\)

b) \(7,8\left( s \right)\)

Giải thích các bước giải:

a) Ta có: 

\(\begin{array}{l}
{a_1} = \dfrac{{{v_1}}}{{{t_1}}} = \dfrac{2}{{10}} = 0,2\left( {m/{s^2}} \right)\\
F - {F_{ms}} = ma\\
 \Rightarrow F - mg\mu  = ma\\
 \Rightarrow F - 800.10.0,1 = 800.0,2\\
 \Rightarrow F = 960N
\end{array}\)

b) Ta có: 

\(\begin{array}{l}
{s_1} = \dfrac{{v_1^2}}{{2{a_1}}} = \dfrac{{{2^2}}}{{2.0,2}} = 10\left( m \right)\\
{s_2} = s - {s_1} = 50 - 10 = 40\left( m \right)\\
1,5F - {F_{ms}} = m{a_2}\\
 \Rightarrow 1,5.960 - 800.10.0,1 = 800.{a_2}\\
 \Rightarrow {a_2} = 0,8\left( {m/{s^2}} \right)\\
{s_2} = {v_1}{t_2} + \dfrac{1}{2}{a_2}t_2^2\\
 \Rightarrow 40 = 2{t_2} + \dfrac{1}{2}.0,8.t_2^2\\
 \Rightarrow {t_2} = 7,8\left( s \right)
\end{array}\)