图甲为儿童玩具小火车轨道,由竖直圆轨道BMC(B、C是圆弧轨道最低点且可认为是紧靠的)、竖直圆弧轨道DE和FH、倾斜半圆轨道EGF、四分之一水平圆轨道AK和IJ与水平轨道AB、CD、HI、KJ平滑相切连接而成,图乙为轨道侧视示意图。已知竖直圆轨道、圆弧DE、HF和EGF的半径均为R=0.4m,CD=0.4m,圆弧DE、FH对应的圆心角
![](https://math.21cnjy.com/MathMLToImage?mml=%3Cmath+xmlns%3D%22http%3A%2F%2Fwww.w3.org%2F1998%2FMath%2FMathML%22%3E%3Cmrow%3E%3Cmo%3E%E2%88%A0%3C%2Fmo%3E%3Cmi%3EH%3C%2Fmi%3E%3Cmsub%3E%3Cmi%3EO%3C%2Fmi%3E%3Cmn%3E3%3C%2Fmn%3E%3C%2Fmsub%3E%3Cmi%3EF%3C%2Fmi%3E%3Cmo%3E%3D%3C%2Fmo%3E%3Cmn%3E37%3C%2Fmn%3E%3Cmo%3E%C2%B0%3C%2Fmo%3E%3C%2Fmrow%3E%3C%2Fmath%3E)
,小火车质量m=0.2kg且可视为质点。水平轨道上小火车受到轨道的阻力恒为其重力的0.2倍,其它轨道的阻力忽略不计。小火车在H点处以恒定功率P=2w由静止开始启动,沿着HIJKAB轨道运动,经过t=2s到达B点时关闭电动机,小火车恰好能沿着竖直圆轨道运动。
![](https://math.21cnjy.com/MathMLToImage?mml=%3Cmath+xmlns%3D%22http%3A%2F%2Fwww.w3.org%2F1998%2FMath%2FMathML%22%3E%3Cmrow%3E%3Cmi%3Esin%3C%2Fmi%3E%3Cmn%3E37%3C%2Fmn%3E%3Cmo%3E%C2%B0%3C%2Fmo%3E%3Cmo%3E%3D%3C%2Fmo%3E%3Cmn%3E0.6%3C%2Fmn%3E%3C%2Fmrow%3E%3C%2Fmath%3E)
,
![](https://math.21cnjy.com/MathMLToImage?mml=%3Cmath+xmlns%3D%22http%3A%2F%2Fwww.w3.org%2F1998%2FMath%2FMathML%22%3E%3Cmrow%3E%3Cmi%3Ecos%3C%2Fmi%3E%3Cmn%3E37%3C%2Fmn%3E%3Cmo%3E%C2%B0%3C%2Fmo%3E%3Cmo%3E%3D%3C%2Fmo%3E%3Cmn%3E0.8%3C%2Fmn%3E%3C%2Fmrow%3E%3C%2Fmath%3E)
。求: