大学里的物理题目 in english!
A stone is released from a balloon that is descending at a constant speed of 10 m/s. Neglecting
air resistance, after 20 s the speed of the stone is:




2160 m/s



1760 m/s



206 m/s



196 m/s



186 m/s

ans: C
为什么为什么!