Practice portal › Laws of Motion › Blocks on Inclines and Wedges
Asked in JEE Main 2005 · Accelerating wedges
Idea: sit in the accelerating frame of the incline. There the block is in equilibrium under gravity, the normal force, and a pseudo-force ma pointing backwards.
Resolve along the slope, where the normal force drops out:
the pseudo-force contributes ma cos α up the slope;
gravity contributes mg sin α down the slope.
For the block to stay put these must cancel:
ma cos α=mg sin α
a=g tan α.
Check the extremes: a flat surface (α→0) needs no acceleration at all, and a vertical wall (α→90°) would need an infinite one — both of which g tan α delivers.
The stem is printed as 'α is equal to', but every option has the dimensions of an acceleration, so what is being asked for is a.
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