Students are asking for the mathematics which they are not understanding in the email; kaacconsultant@gmail.com . Solution is appearing in this page for helping others also.
The problem is The slant height of a right circular cone is 10 m and its height is 8 m. find the area of the curved surface.
right circular cone means ,its base is a circle the meaning of the right is , its peak is straight at 90 degrees. above the center of the base .
slant height means ,distance of the peak from the any point of base perimeter
height is 8 meter
slant height is 10 meter
from the above data we have to deduce another date , which is the radius of the base, otherwise we will not be able to find curved surface area.
radius of the base is 6 meter. ( I have not deduced the same , students have to apply their skill) if not otherwise contact.
Now area of the curved surface is pi * radius* slant height value of pi has taken as = 3.142
which will become 187.52 sq meter why square meter ? because to units of meters has been multiplied.
Suppose there are two spheres having radius R and r , is there any relation can be established with this two radius. let us try
Surface area of the sphere with radius R = 4 * pi* R2 ( R square)
similarly surface area of the sphere with radius r = 4*pi* r2 ( r square)
ratio is coming as R2 / r2 or (R/r)2
| Problem | ||||||||||
| A cylindrical shaped article has a height of 20 Cm.The radius of its base is 21 cm. and its volume is | ||||||||||
| 2310 cm 3 | ||||||||||
| It is open at the top | ||||||||||
| Find the cost of painting it from otside when rate is Rs. 5 per Cm 2 | ||||||||||
| Solution | ||||||||||
| Given data : | ||||||||||
| Height H | 20 Cm | |||||||||
| Radius of the base R | 21 Cm | |||||||||
| Volume V | 2310 cm 3 | |||||||||
| Now as the cylinder is open at the top , surface area we have to find out at the cylinder wall and the bottom | ||||||||||
| surface area of the cylinder | 2 π R L | |||||||||
| 2640 | cm 2 | |||||||||
| surface area of the bottom | π R 2 | |||||||||
| 1386 | cm 2 | |||||||||
| Total area to be painted | surface + bottom | |||||||||
| 4026 | cm 2 | |||||||||
| And cost of painting is Rs. 5 per square Cm | ||||||||||
| That is one square Cm will cost Rs. 5 | ||||||||||
| But we have 4026 | cm 2 | Rs. | 5*4026 | cm 2 | ||||||
| Rs. | 20,130 | will be cost. | ||||||||
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