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v0=9.8m/sï¼æ°´å¹³åév0x=9.8Ãcosθ=9.8Ãcos30°=4.9â3m/s
ç«ååév0y=9.8Ãsinθ=9.8Ãsin30°=4.9m/s
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x=4.9â3t
y=4.9t-4.9t²
y=-xâ3/3
4.9t-4.9t²=-4.9â3tâ3/3
1-t=-1
t=2
y=4.9t-4.9t²=4.9tï¼1-tï¼=9.8ï¼1-2ï¼=-9.8
OB=2|y|=19.6m
ï¼2ï¼t=1.5ï¼
x't=4.9â3,y't=4.9-9.8t=-9.8
v=âï¼x't²+y't²ï¼=âï¼4.9²Ã3+9.8²ï¼=12.96m/sï¼
ä¸xè½´æ£æ¹å夹è§=arctanï¼y't/x'tï¼=arctanï¼-9.8/4.9â3ï¼=arctanï¼-2/â3ï¼=-49.11°ï¼
ä¸yè½´è´å夹è§90-49.11=40.89°
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