- #1
jiboom
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a bead of mass m can slide without friction along a circular hoop of radius a which is fixed in a vertical plane. the bead is connected to the highest point of the hoop by a light elastic string of natural length a and modulus 3mg. initially the bead is moving with speed u through the lowest point point of the hoop. given that u^2=ag, show that the bead just reaches the highest point of the hoop. show that the speed was u at the instant when the string first went slack and find the reaction of the hoop on the bead at that instant.
i think i have done the first part.
i used energy to find the velocity at the top then resolved at the top to get
T+mg=mg which gives T=0 so complete circle just,BUT i have no reaction. do i not have a reaction force here?if i put R in i could just have R=-T?
for the second part i am lost. any help would be appreciated. what equations do i get to show when string goes slack speed is u? how do i put R into this?
2)
the ends of a light string are fixed to 2 points A B in the same vertical line with A above B,and the string passes through a small smooth ring of mass . the ring is fastened to the string at a point P and when the string is taut the angle APB is a right angle,the angle BAP is T and AB=5a AP=4a. the ring revolves in a horizontal circle with constant angular velocity w and with the string taut.
if the ring is free to move on the string,instead of being fastened, show that it will remain in the same position on the string if the angular velocity,w,satisifies
12aw^2=35g
once again,have no idea how to set up the equations of motion. do i have only a reaction and no tension? how does the reaction work? what condition do i need for it not to move??
i think i have done the first part.
i used energy to find the velocity at the top then resolved at the top to get
T+mg=mg which gives T=0 so complete circle just,BUT i have no reaction. do i not have a reaction force here?if i put R in i could just have R=-T?
for the second part i am lost. any help would be appreciated. what equations do i get to show when string goes slack speed is u? how do i put R into this?
2)
the ends of a light string are fixed to 2 points A B in the same vertical line with A above B,and the string passes through a small smooth ring of mass . the ring is fastened to the string at a point P and when the string is taut the angle APB is a right angle,the angle BAP is T and AB=5a AP=4a. the ring revolves in a horizontal circle with constant angular velocity w and with the string taut.
if the ring is free to move on the string,instead of being fastened, show that it will remain in the same position on the string if the angular velocity,w,satisifies
12aw^2=35g
once again,have no idea how to set up the equations of motion. do i have only a reaction and no tension? how does the reaction work? what condition do i need for it not to move??