Đáp án:
\(\begin{array}{l}
33.B. - 16J\\
a = \dfrac{{v{'^2} - {v^2}}}{{2s}} = \dfrac{{0 - {4^2}}}{{2.0,8}} = - 10m/{s^2}\\
{F_{ms}} = - ma = - 2.( - 10) = 20N\\
{A_{ms}} = {F_{ms}}.s.\cos 180 = 20.0,8.\cos 180 = - 16J\\
34.C.250W\\
F = P = 50N\\
A = Fs = 50.10 = 500J\\
P = \dfrac{A}{t} = \dfrac{{500}}{2} = 250W\\
35.A.5,{82.10^4}W\\
F = ma = 1100.4,6 = 5060N\\
s = \dfrac{1}{2}a{t^2} = \dfrac{1}{2}.4,{6.5^2} = 57,5m\\
A = Fs = 5060.57,5 = 290950J\\
P = \dfrac{A}{t} = \dfrac{{290950}}{5} = 58910W \sim 5,{82.10^4}W\\
36.D.0,8s\\
F - {F_{ms}} = 0 \Rightarrow F = {F_{ms}} = \mu mg = 0,5.800 = 400N\\
A = Fs = 400.10 = 4000J\\
P = \dfrac{A}{t} \Rightarrow t = \dfrac{A}{P} = \dfrac{{4000}}{{5000}} = 0,8s\\
38.P = 0,5W\\
A = Ph = 50.1,2 = 60J\\
P = \dfrac{A}{t} = \dfrac{{60}}{{2.60}} = 0,5W\\
39.D.1kW\\
P = 500.20 = 10000N\\
A = Ph = 10000.6 = 60000J\\
P = \dfrac{A}{t} = \dfrac{{60000}}{{60}} = 1000W = 1kW\\
\end{array}\)
