Question

The two blocks in an Atwood machine have masses $2.0kg$ and $3.0kg$ . Find the work done by gravity during the fourth second after the system is released from rest :-

• A. $70J$
• B. $210J$
• C. $140J$
• D. $-140J$

Answer 1

Answer: (A)

$a=\frac{3 - 2}{3 + 2}g=\frac{g}{5}$
Distance covered in fourth second
$=\frac{\left(2 n - 1\right)}{2}=\frac{\left(2 \times 4 - 1\right) \times g}{2 \times 5}=\frac{7 g}{10}$
Hence, work done by gravity $=\left(m_{2} - m_{1}\right)gh$
$=\left(3 - 2\right)g\times \frac{7 g}{10}=\frac{7}{10}g^{2}$