IIT JEE Advanced 2011 Paper 1

As depicted in the two figures here, let us consider that F1 is the force applied to pull the body upwards:
F1 = mg (sin θ + µ cos θ)
and F2 is the force applied to keep the body in position):
F2 : mg (sin θ - µ cos θ)

However, we have
F1 = 3F2
mg (sin θ + µ cos θ) = 3mg (sin θ - µ cos θ)
4µ cos θ = 2 sin θ
⇒ µ =

1

2

(Since θ = 45°)
Therefore, N = 10μ = 5.