question_answer 38)

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

Answer:

At the highest point of the death-well, the normal action R of the walls of the chamber acts downwards. The centripetal force is provided by his weight mg and the normal reaction R.                             The motorcyclist does not fall down due to the balancing of these forces. For minimum speed, at the highest point, R = 0, so that   or