In the figure shown  $m_1=1kg,m_2=2kg$, pulley is ideal. At t = 0, both masses touches the ground and string is taut. A force F = 2t is applied to pulley (t is in second) then $(g=10m/s^2)$

Acceleration of pulley when m2 is about to lift off is $5m/s^2$

$m_1$  is lifted off the ground at t = 10 secs

$m_2$  is lifted off the ground at  t = 20 secs

Both blocks are lifted off simultaneously