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Câu 219: C

Ta có: 

\(\begin{array}{l}
mgl\sin \alpha  = \dfrac{1}{2}m{v^2}\\
 \Rightarrow v = \sqrt {2gl\sin \alpha }  = \sqrt {2.10.10.\sin 60}  = 13,16\left( {m/s} \right)
\end{array}\)

Câu 220: D

Ta có:

\(\begin{array}{l}
P\sin \alpha  - {F_{ms}} = ma\\
 \Rightarrow mg.\dfrac{h}{l} - {F_{ms}} = ma\\
 \Rightarrow 3.9,8.\dfrac{{0,5}}{1} - 5 = 3.a\\
 \Rightarrow a = 3,23\left( {m/{s^2}} \right)\\
v = \sqrt {2al}  = \sqrt {2.3,23.1}  = 2,54\left( {m/s} \right)
\end{array}\)