WAEC Physics 2015 Paper

Concept:The vertical components of the two equal tensions must balance the weight of the bucket.Explanation:Let the tension in each string be $T$.Each string makes an angle of $30^\circ$ with the horizontal.So, the vertical component of each tension is $T \sin 30^\circ$.Since there are two strings, the total upward vertical force is $2T \sin 30^\circ$.For equilibrium, this total upward force equals the weight of the bucket:$$2T \sin 30^\circ = 20\,\mathrm{N}$$We know $\sin 30^\circ = \frac{1}{2}$.Substituting gives:$$2T \times \frac{1}{2} = 20\,\mathrm{N}$$$$T = 20\,\mathrm{N}$$Thus, the tension in each string is $20\,\mathrm{N}$.Answer:$T = 20\,\mathrm{N}$ (Option B)