Volumes and Surface Area of Solids, Ex- 20B

Question

15. A piece of ductile metal is in the form of a cylinder of diameter 1 cm and length 11 cm. It is drawn out into a wire of diameter 1 mm. What will be the length of the wire so obtained? 

19. A road roller takes 750 complete revolutions to move once over to level a road. Find the area of the road if the diameter of the road roller is 84 cm and its length is 1 m.

Can anyone please send me the answers of the q no. 15 and 19?

Answer 1

15. Please see the below question:

https://www.sarthaks.com/1146142/piece-ductile-metal-the-form-cylinder-diameter-and-length-it-drawn-out-into-wire-diameter

19. 

Since the wheel of a road roller is cylindrical in shape,

In one revolution, the roller will cover an area equal to its lateral surface area.

Radius of the road roller r = 84/2 cm = 42 cm

Length of the road roller, h = 1 m = 100 cm

In 1 revolution, area of the road covered = 2πrh 

= 2 × 22/7 × 42 × 100

= 26400 cm² = 2.64 m²

In 750 revolutions area of the road covered 

= 750 × 2.64 m² = 1980 m²