Rankers Physics

A cubical block of mass m and edge a slides down a rough inclined plane of inclination θ with a uniform speed. Find the torque of the normal force acting on the block about its centre

m g a sin θ
(m g a sin θ)/3
(m g a sin θ)/4
(m g a sin θ)/2

Solution:

As the object slides with constant speed friction force is balancing mgsinθ. Torque of Normal reaction and  friction force about centre of object will cancel each other.

τ=mg.sinθ × a/2 = (mg a sinθ)/2

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