美国的“卡西尼”号探测器经过长达7年的“艰苦”旅行,进入绕土星飞行的轨道.若“卡西尼”号探测器在半径为R的土星上空离土星表面高h的圆形轨道上绕土星飞行,环绕n周飞行时间为t.已知万有引力常量为G,则下列关于土星质量M和平均密度ρ的表达式正确的是( )
A:M=4π2n2(R+h)3Gt2,ρ=3πn2(R+h)3Gt2R3
B:M=4π2(R+h)2Gt2,ρ=3πn2(R+h)2Gt2R3
C:M=4π2t2(R+h)3Gn2,ρ=3πt2(R+h)3Gn2R3
D:M=4π2n2(R+h)3Gt2,ρ=3π(R+h)3Gt2R3
一辆在水平路面上沿直线匀速行驶的货车,行驶时所受的阻力为车总重的0.1倍,货车(含驾驶员)空载时重为2.5×104N.
(1)求货车空载行驶时所受的阻力大小;
(2)求货车以72km/h的速度空载匀速行驶时,10s内货车牵引力做的功;
(3)推导公式P=Fv.
(4)当货车以90kW的额定功率、90km/h的速度匀速行驶时,求货车最多可装载多重的货物.
( + )÷ = (秒).
答:火车通过大桥一共需要 秒.
读图,回答下题
Our Trip to Yibin City
When
On Friday.
How
We will go there 1.
What
But you will need to bring 2 .
Where
Then in the afternoon we will go to 3.
What time
⑴Now please remember that the bus will leave right at 4 .
⑵Tell your parents we'll be back at school 5.