Question : A right square pyramid having a lateral surface area is 624 cm2. If the length of the diagonal of the square is $24 \sqrt{2}$, then the volume of the pyramid is:
Option 1: 1150 cm3
Option 2: 780 cm3
Option 3: 1083 cm3
Option 4: 960 cm3
Correct Answer: 960 cm 3
Solution : Given: Length of the diagonal of the square = $24\sqrt2$ Let the side of the square be $a$. We know that, Length of the diagonal of the square = $a\sqrt2$ Thus, $24\sqrt2=a\sqrt2$ $\therefore a = 24$ cm Perimeter of square = 24 × 4 = 96 cm Area of the square = 24 × 24 = 576 cm 2 Given: Lateral surface area of pyramid = 624 cm 2 We know that, Lateral surface area of pyramid = $\frac{1}{2}$ × perimeter of base × slant height ⇒ $624 = \frac{1}{2}×96$ × slant height $\therefore$ Slant height = $\frac{624\times2}{96}= 13$ cm Now, Height = $\sqrt{\text{slant height}^2-{(\frac{\text{side of square}}{2}})^2}$ = $\sqrt{13^2-12^2}$ = $\sqrt{169-144}$ = $5$ cm Volume of the pyramid = $\frac{1}{3}$× area of base × height = $\frac{1}{3}\times576\times5$ = $960$ cm 3 Hence, the correct answer is 960 cm 3 .
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