A balloon starting from rest ascends vertically with uniform acceleration to a height of 100 m in 10 sec. The force on the bottom of the balloon by a mass of 50 kg is $( g=10\: ms^{-2})$
$\begin {array} {1 1} (1)\;100\: N & \quad (2)\;300\: N \\ (3)\;600\: N & \quad (4)\;400\: N \end {array}$