You may have seen in a circus a motorcyclist driving in vertical loops inside a death well (a hollow spherical chamber with holes so the spectators can watch from outside) Explain clearly why the motorcyclist does not drop down when he is at the uppermost point of death well with no support from below What is the minimum speed required at the uppermost position to perfrom a vertical loop if the radius of the chamber is 25 m ?

Explanation

At the uppermost point of the death well with no support from below the motorcyclist does not drop down This is because his weight is being balanced by the centrifugal force Infact the weight of the motorcyclist is spent up in providing the necessary centripetal force to the motorcyclist and hence he does not drop down .
At the uppermost point `R + mg = (m upsilon^(2))/(r)` where R is the normal reaction (downwards) on the motorcyclist by the ceilling of the chamber
Speed will be minimum , when `R = 0 :. mg = (m upsilon^(2))/(r)` or `upsilon = sqrt( rg) = sqrt(25 xx 10) = 15.8 m//s` .