Đáp án:

Phong nha cave is a world heritage site .The full name of that cave is Phong nha ke bang belong to Ke bang mountains in Quang Binh Phong Nha-Ke Bang area is noted for its cave and grotto systems as it is composed of 300 caves and grottos, of which only 20 have been surveyed by Vietnamese and British scientists; 17 of these are in located in the Phong Nha area and three in the Ke Bang area. Phong Nha holds several world cave records, as it has the longest underground river, as well as the largest caverns and passageways.

The park derives it name from Phong Nha cave, the most beautiful of all, containing many fascinating rock formations, and Ke Bang forest

The plateau on which the park is situated is probably one of the finest and most distinctive examples of a complex karst landform in Southeast Asia.

This national park was listed in UNESCO’s World Heritage Sites in 2003 for its geographical values as defined in its criteria viii.

Giải thích các bước giải:

Đáp án:

$\begin{array}{l}
{a_o} = 0,2m/{s^2}\\
T = 49N
\end{array}$ 

Giải thích các bước giải:

Gia tốc của vật m và lực căng dây là:

$\begin{array}{l}
\left\{ \begin{array}{l}
 - T + mg = m{a_o}\\
\dfrac{T}{2} - {m_1}g =  - {m_1}a' + {m_1}{a_o}\\
\dfrac{T}{2} - {m_2}g = {m_2}a' + {m_2}{a_o}
\end{array} \right.\\
 \Leftrightarrow \left\{ \begin{array}{l}
5{a_o} + T = 50\\
 - 3{a_o} + 3a' + \dfrac{T}{2} = 30\\
 - 2{a_o} - 2a' + \dfrac{T}{2} = 20
\end{array} \right.\\
 \Leftrightarrow \left\{ \begin{array}{l}
{a_o} = 0,2m/{s^2}\\
a = 2m/{s^2}\\
T = 49N
\end{array} \right.
\end{array}$