Ncert Exercises & Solutions

Q. 29 Block A of weight 100 N rests on a frictionless inclined plane of slope angle 30 $°$ . A flexible cord attached to A passes over a frictionless pulley and is connected to block B of weight w. Find the weight w for which the system is in equilibrium.

Hint: Balance the forces.

Step 1: Write the equations for both of the blocks and find w.

In equilibrium, the force

mgsinθ

acting on block A parallel to the plane should be balanced by the tension in the string
mg sin

θ

= T = F [

∵

T = F given] ...(i)
and for block B, w = T = F ...(ii)
where. w is the weight of block B.
From Eqs. (i) and (ii). we get,

\begin{array}{l} ∴ w = mg \sin θ \\ = 100 \times \sin 30^{\circ} (∵ mg = 100 N) \\ = 100 \times \frac{1}{2} N = 50 N \end{array}

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