Question

some plastic balls of radius 1cm were melted and cast into a tube the thickness, length and outer radius of the tube were 2cm 90cm and 30cm respectively how many balls were melted to make the tube

Answer 1

15 is the answer because radius of one ball is 1 cm and the tube was formed by30 radius

Answer 2

Answer:

No of balls are 7830.

Step-by-step explanation:

Given: Radius of plastic ball, r = 1 cm

           Thickness of tube = 2 cm

           Length of Tube, h = 90 cm

           Outer radius of Tube, $r_2$ = 30 cm

To find: No. of Balls

Volume of a ball = volume of sphere

                            = $\frac{4}{3}\pi r^3$

                            = $\frac{4}{3}\times\frac{22}{7}\times1^3$

                            = $\frac{88}{21}\:cm^3$

Inner radius of tube, $[r_1$ = 30 - 2 = 28 cm

Volume of tube = Volume of Outer cylinder - Volume of Inner Cylinder

                          = $\pi r_2^2h-\pi r_1^2h$

                          = $\pi h(r_2^2-r_1^2)$

                          = $\frac{22}{7}\times90\times(30^2-28^2)$

                          = $\frac{229680}{7}\:cm^3$

$No.\:of \:Balls\:=\:\frac{Volume\:of\:tube}{Volume\:of\:1\:ball}$

                               $=\:\frac{\frac{229680}{7}}{\frac{88}{21}}$

                               $=\:\frac{229680\times3}{88}$

                               $=\:7830$

Therefore, No of balls are 7830.