Why do tyres have a better griop of the road while going on a level road than while going on an incline?

Why the passengers are advised to remove the ink from their pens while going up to in an aeroplane ?

A plumb bob is hung from the ceiling of a train compartment. If the train moves with an acceleration a along a straight horizontal track, the string supporting the bob makes an angle tan^1 (a/g) with the normal to the ceiling. Suppose the train moves on an inclined straight track with uniform velocity, if the angle of incline is tan^-1(a/g) , the string again makes the same angle with the normal to the ceiling. Can a person sitting inside the compartment tell by looking at the plumb line whether the train is accelerated on a horizontal straight track or it is going on an incline? If yes, how? If no, suggest a method to do so.

When and why do snails go into aestivation?

Find the maximum speed at which a car can turn round a curve of 36 m radius on a level road. Given the coefficient of friction between the tyre and the road is 0.53.