A motor cyclist wants to drive in horizontal circles on the vertical inner surface of a large cylindrical wooden well of radius $$8.0 \mathrm{~m}$$, with minimum speed of $$5 \sqrt{5} \mathrm{~ms}^{-1}$$. The minimum value of coefficient of friction between the tyres and the wall of the well must be $$\left(g=10 \mathrm{~ms}^{-2}\right)$$

Assertion (A) Two identical trains move in opposite senses in equatorial plane with same speeds relative to the Earth’s surface. They have equal magnitude of normal reaction.

Reason (R) The trains have different centripetal accelerations due to different speeds.