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As shown in the given figure… (Class 10 Maths 2026, Q34b)

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MathsCBSE Class 10 · Standard · Board exam 2026, set 30/2/1 · 5 marks · Long answer

CBSE Class 10 Mathematics Standard 2026: question 34(b)

Set in the CBSE Class 10 board exam of 2026, paper 30/2/1, section D, question 34(b), for 5 marks. Try it first; the hints and our step-by-step solution are below.

Q34(b) · 5 marks · Long answerCompetency-basedSome Applications of Trigonometry

As shown in the given figure, a girl of height 90 cm is walking away from the base of a lamp post at a speed of 1·2 m/s. If the lamp is 3·6 m above the ground, find the length of her shadow after 4 seconds.

Figure in the paper: Right triangle ABE: A at top of lamp post, B at base (right angle at B), AB = 3·6 m vertical. E is on the ground to the right of B. Point C lies on AE; CD is vertical with D on BE, right angle at D, and CD = 90 cm representing the girl. BD is the girl's distance from lamp base; DE is her shadow. See it in the official paper.

Source: official question paper from cbse.gov.in (PDF). See it in the full 2026 board paper, set 30/2/1.

Hints

Open one hint at a time and try again before the next.

Hint 1

First find how far she walks in 4 seconds, and change 90 cm into metres.

Hint 2

The lamp-post triangle and the girl's triangle share angle E and both have a right angle.

Step-by-step solution

Each step shows the marks it earns, as an examiner would award them. Checked by an independent re-solve from the question paper.

  1. Distance walked in 4 s: m. Girl's height CD = 90 cm = 0.9 m.

    1 mark

  2. In △ABE and △CDE: and is common, so (AA similarity).

    2 marks

  3. ½ mark

  4. 1 mark

  5. m. Length of her shadow after 4 s = 1.6 m.

    ½ mark

Answer: 1.6 m

Where the marks are

  • Finds BD = 4.8 m (1 mark)
  • Proves △ABE ∼ △CDE by AA (2 marks)
  • Writes ratio BE/DE = AB/CD (½ mark)
  • Substitutes with BE = 4.8 + DE (1 mark)
  • Gets DE = 1.6 m (½ mark)

Revise the chapter

Practise this chapterBoard-style questions from Some Applications of Trigonometry, one at a time, marked against the answer key and marking points.Back to the full paper2026 board paper, set 30/2/1 (Standard): every question, by section.

The question is transcribed from the official paper; figures are described in words. The solution, hints and chapter tag are ours. Spotted an error? Write tosupport@questionbuddy.in.