质量为m=0.10kg的小钢球以v0=10m/s的水平速度抛出，下落h=5.0m时撞击一钢板，撞后速度恰好反向，则钢板与水平面的夹角θ=______．刚要撞击钢板时小球动量的大小为______．
（取g=10m/s2）
由于小球下落过程中在竖直方向有h=
gt2，解得t=1 2
=1s，2h g
故落到钢板上时小球在竖直方向的速度vy=gt=10m/s，
则有tanθ=
=v0 vy
=110 10
解得钢板与水平面的夹角θ=45°．
小球落到钢板上时的速度v=
=10vo2+vy2
m/s2
故小球的动量大小P=mv=0.1×10
=2
kg?m/s．2
故答案为：45°；
kg?m/s．2
| 完型填空。 | ||||
| One day a farmer's donkey (驴) fell down into a well (井). The animal cried 1 for hours as the farmer tried to find a 2 way to save him. But finally the farmer decided the animal was 3 and the well needed to be 4 up anyway, so the donkey just wasn't 5 saving. He 6 all his neighbours to come over and help him. They all grabbed (握起) a shovel (铁铲) and began to shovel 7 into the well. At first, the donkey 8 what was happening and cried loudly. Then, to everyone's surprise, he was 9 . A few shovel loads later, the farmer looked 10 and was shocked at what he 11 . With every shovel of dirt that 12 his back, the donkey was doing something amazing. He would 13 it off and take a step up. As the farmer's neighbors 14 to shovel dirt on top of the animal, he would shake it off and take another 15 up. Pretty soon, everyone was surprised as the donkey stepped up over the entrance of the 16 and ran off. Life is going to shovel dirt on you, all kinds of dirt. The best way of 17 out of the well is to shake it off and take a step up. Each of our 18 is a stepping-stone. We can get out of the 19 wells just by not stopping. 20 give up! Shake it off and take a step upward! | ||||
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