NCERT Exemplar Solutions
Class 7 - Mathematics - Unit 1: Number System - Multiple Choice QuestionsQuestion 11
Class 7 - Mathematics - Unit 1: Number System - Multiple Choice Questions
Question. 11
Water level in a well was 20 m below ground level. During rainy season, rain water collected in different water tanks was drained into the well and the water level rises 5 m above the previous level. The wall of the well is 1 m 20 cm high and a pulley is fixed at a height of 80 cm. Raghu wants to draw water from the well. The minimum length of the rope that he can use is
17 m
18 m
96 m
97 m
Detailed Answer with Explanation:
Beginner-friendly steps:
Step 1: Find the new water level (depth below ground).
Originally, water is 20 m below ground.
It rises by 5 m after rain.
(20 ;-; 5)
(=; 15 ext{m below ground})
Step 2: Find the pulley height above ground.
Wall height = 1 m 20 cm = (1.20 ext{m})
Pulley is 80 cm above the wall top = (0.80 ext{m})
Total pulley height above ground:
(1.20 ;+; 0.80)
(=; 2.00 ext{m})
Step 3: Minimum rope length.
Rope must reach from the pulley down to the water surface.
That distance = depth of water below ground + pulley height above ground.
(15 ;+; 2)
(=; 17 ext{m})
Answer: 17 m (Option a)