Q.

A car is negotiating a curved road of radius R. The road is banked at an angle θ. The coefficient of friction between the tyres of the car and the road is μs. The maximum safe velocity on this road is              [2016]
 

1 gR μs+tanθ1-μstanθ  
2 gR2 μs+tanθ1-μstanθ  
3 gR2 μs+tanθ1-μstanθ  
4 gR μs+tanθ1-μstanθ  

Ans.

(4)

For vertical equilibrium on the road,

        Ncosθ=mg+fsinθmg=Ncosθ-fsinθ            ...(i)

Centripetal force for safe turning,  Nsinθ+fcosθ=mv2R        ...(ii)

From eqns. (i) and (ii), we get

v2Rg=Nsinθ+fcosθNcosθ-fsinθvmax2Rg=Nsinθ+μsNcosθNcosθ-μsNsinθ

vmax=Rg(μs+tanθ1-μstanθ)