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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

Asked in NEET 2016 Phase-I · Banked roads and the conical pendulum

Answer: (4) √gR·(μₛ+tan θ)/(1-μₛ tan θ)

Step-by-step solution

Given: banked road of radius R and angle θ, tyre friction μₛ.

Idea: at the maximum speed the car is on the point of sliding up the bank, so friction acts down the slope and adds to the horizontal pull of the normal force.

Along the vertical: N cos θ=mg+μₛN sin θ.

Along the horizontal, towards the centre: N sin θ+μₛN cos θ=(mv²)/R.

Dividing the second by the first removes N and m: (v²)/(Rg)=(sin θ+μₛ cos θ)/(cos θ-μₛ sin θ).

Dividing top and bottom by cos θ: (v²)/(Rg)=(tan θ+μₛ)/(1-μₛ tan θ).

vₘₐₓ=√gR·(μₛ+tan θ)/(1-μₛ tan θ).

Why the other options are wrong

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