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phy4 help

can someone explain the last question to me?

the answer says..
When the chain of the swing is horizontal, the weight of the child acts downwards (1)
centripetal force is zero (1)


why is centripetal force zero?
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Reply 1
Avatar for rbnphlp
rbnphlp
11
old_skool
can someone explain the last question to me?

the answer says..
When the chain of the swing is horizontal, the weight of the child acts downwards (1)
centripetal force is zero (1)


why is centripetal force zero?

To answer ur q, consider the lowest point at which the swing starts to be PE=0 , as it gains a height of 3m from the lowest point (KE=max) all the Ke wil be converted into PE at wen the swing is horizontail ,which means it has v=o.. and therefore ,T=mv^2/r
so if v= 0 the no tension , and therefore no centripetal force...


however sayin all this I cant see how they answered the q
Reply 2
Avatar for old_skool
old_skool
OP
rbnphlp
To answer ur q, consider the lowest point at which the swing starts to be PE=0 , as it gains a height of 3m from the lowest point (KE=max) all the Ke wil be converted into PE at wen the swing is horizontail ,which means it has v=o.. and therefore ,T=mv^2/r
so if v= 0 the no tension , and therefore no centripetal force...


however sayin all this I cant see how they answered the q


oo thanks for the help

so when the swing is horizontal..there is no KE so v = 0 so centripetal force is 0 by mv^2/r

but there is still a normal contact force from the seat of the swing acting towards the centre..and weight acting downwards right?

so the child may lose contact with the seat because the normal contact force isn't balanced by the centripetal force?
Reply 3
Avatar for rbnphlp
rbnphlp
11
old_skool
oo thanks for the help

so when the swing is horizontal..there is no KE so v = 0 so centripetal force is 0 by mv^2/r

but there is still a normal contact force from the seat of the swing acting towards the centre..and weight acting downwards right?

so the child may lose contact with the seat because the normal contact force isn't balanced by the centripetal force?

oh dear ur truly rite ,, I was imaginig the swing a particle and thught the reaction force is acting vertically upwards(ooposite to the weight)...:smile:
And also my orignal eq was wrong , so at horizontal It shuld be R+T=mv^2/r
Yeah at the lowest point R is equal to the weight as centripetal force acts towards the centre.
So, R+T=mg

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