问题描述：
1.A 0.25g flea sits on a disc at a distance of 4cm from the center of the disc.if the disc rotates at 67 rpm and the flea is just able to maintain its position without sliding,determine the coefficient of static friction between the flea and the disc that enables the flea to maintain its uniform circular motion.
2.Snoopy is flying his vintage war plane in loop the loop path chasing the red Baron.his instruments tells him that the plane is level (at the bottom of the loop) and travelling at a speed of 180km/h.he is sitting on a bathroom scale,and notes that it reads four times the normal force of gravity on him.what is the radius of the loop?
3.As an indication of the size of the sun's gravitational pull on earth,carry out the rough calculations that follow.suppose that the sun's gravitational attraction could be replaced by a steel wire,running from the sun to the earth,with the wire's tension holding the earth in its orbit.good steel has a breaking stress of 5.0x10^8N/m^2 of cross section area.
a)calculate the cross-section area of wire that could just hold the earth in its orbit.
b)calculate the corresponding wire diameter.
4.By looking at distance galaxies,astronnomers have conclude that our solar system is circling the center of our galaxie.the hub of this galaxie is lacated about 2.7x10^20m from our sun,and our sun circles the center about every 200 million years.we assume that our sun is attracted by a large number of stars at the hub of the galaxy,and that the sun is kept in orbit by the garavitational attraction of these stars.
a)calculate the total masss of the star at the hub of our galaxy
b)based on an average size star of mass 2.0x10^30kg,determine the approximate number of such stars at the hub
请把公示写清楚点 不要只给我答案
可以用以下公示：
Fnet=mxa
Fc=mxac
Fg=mg
Fg=Gm1m2/d^2
脑子不太好使 呵呵 帮下忙
2.Snoopy is flying his vintage war plane in loop the loop path chasing the red Baron.his instruments tells him that the plane is level (at the bottom of the loop) and travelling at a speed of 180km/h.he is sitting on a bathroom scale,and notes that it reads four times the normal force of gravity on him.what is the radius of the loop?
3.As an indication of the size of the sun's gravitational pull on earth,carry out the rough calculations that follow.suppose that the sun's gravitational attraction could be replaced by a steel wire,running from the sun to the earth,with the wire's tension holding the earth in its orbit.good steel has a breaking stress of 5.0x10^8N/m^2 of cross section area.
a)calculate the cross-section area of wire that could just hold the earth in its orbit.
b)calculate the corresponding wire diameter.
4.By looking at distance galaxies,astronnomers have conclude that our solar system is circling the center of our galaxie.the hub of this galaxie is lacated about 2.7x10^20m from our sun,and our sun circles the center about every 200 million years.we assume that our sun is attracted by a large number of stars at the hub of the galaxy,and that the sun is kept in orbit by the garavitational attraction of these stars.
a)calculate the total masss of the star at the hub of our galaxy
b)based on an average size star of mass 2.0x10^30kg,determine the approximate number of such stars at the hub
请把公示写清楚点 不要只给我答案
可以用以下公示：
Fnet=mxa
Fc=mxac
Fg=mg
Fg=Gm1m2/d^2
脑子不太好使 呵呵 帮下忙
问题解答：
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