The areas of three adjacent faces of a cuboid are in the ratio 7 : 10 : 14. If…

2016

The areas of three adjacent faces of a cuboid are in the ratio 7 : 10 : 14. If the volume of the cuboid is 350 cm³, then the length of the longest side is

  1. A.

    7 cm

  2. B.

    14 cm

  3. C.

    10 cm

  4. D.

    20 cm

Show answer & explanation

Correct answer: C

Let the dimensions of the cuboid be l, b, h. The areas of three adjacent faces are lb, bh, and lh. Given that these areas are in the ratio 7 : 10 : 14.

Let lb = 7k, bh = 10k, and lh = 14k for some constant k.

Multiplying the three face areas: (lb)(bh)(lh) = (7k)(10k)(14k) = 980k³.

This product is equal to (l b h)² = V², where V is the volume.

Given V = 350 cm³, so V² = 350² = 122500.

Therefore, 980k³ = 122500.

Solving for k: k³ = 122500 / 980 = 125 → k = 5.

Now, substitute k = 5: lb = 35, bh = 50, lh = 70.

Using volume V = lbh = 350, and lb = 35, we get h = 350 / 35 = 10 cm.

From bh = 50 and h = 10, we get b = 5 cm.

From lb = 35 and b = 5, we get l = 7 cm.

The dimensions are l = 7 cm, b = 5 cm, h = 10 cm. The longest side is 10 cm.

हिन्दी उत्तर:

माना घनाभ के आयाम l, b, h हैं। तीन संलग्न फलकों के क्षेत्रफल lb, bh, lh हैं। दिया गया है कि ये क्षेत्रफल 7 : 10 : 14 के अनुपात में हैं।

माना lb = 7k, bh = 10k, और lh = 14k, जहाँ k कोई नियतांक है।

तीनों फलकों के क्षेत्रफलों का गुणनफल: (lb)(bh)(lh) = (7k)(10k)(14k) = 980k³।

यह गुणनफल (l b h)² = V² के बराबर है, जहाँ V आयतन है।

दिया गया है V = 350 सेमी³, इसलिए V² = 350² = 122500।

इसलिए, 980k³ = 122500।

k के लिए हल करने पर: k³ = 122500 / 980 = 125 → k = 5।

अब k = 5 रखने पर: lb = 35, bh = 50, lh = 70।

आयतन V = lbh = 350 का उपयोग करने पर, और lb = 35, हमें h = 350 / 35 = 10 सेमी मिलता है।

bh = 50 और h = 10 से, b = 5 सेमी मिलता है।

lb = 35 और b = 5 से, l = 7 सेमी मिलता है।

आयाम l = 7 सेमी, b = 5 सेमी, h = 10 सेमी हैं। सबसे लंबी भुजा 10 सेमी है।

A video solution is available for this question — log in and enroll to watch it.

Explore the full course: Uptet Paper 1