—Father's Day is coming. Could you tell me ________? —What about a watch? He'll like it.
一个载重气球在空气中匀速上升时，受到的浮力为2000N，若在所载重物中再加200N的物体，这时气球就能匀速下降，假设气球上升和下降时所受的浮力和阻力大小不变，则气球的重力为 ____ N，受到的阻力为 ____ N．
