Advertisements
Advertisements
प्रश्न
A golf ball has diameter equal to 4.2 cm. Its surface has 200 dimples each of radius 2 mm. Calculate the total surface area which is exposed to the surroundings assuming that the dimples are hemispherical.
उत्तर
Surface area of ball
`=4pir^2`
`=4pi (4.2 /2)^2`
`= 17.64 pi cm^2`
Total surface area exposed
SA of ball `- 200 (pir^2 - (4pir^2)/2)`
`=17.64 pi - 200 pir^2`
`=17.64 pi -8pi`
`= 80.5 cm^2`
APPEARS IN
संबंधित प्रश्न
A solid metallic sphere of radius 5.6 cm is melted and solid cones each of radius 2.8 cm and height 3.2 cm are made. Find the number of such cones formed.
A factory manufactures 120,000 pencils daily . The pencil are cylindrical in shape each of length 25 cm and circumference of base as 1.5 cm . Determine the cost of colouring the curved surfaces of the pencils manufactured in one day at ₹0.05 per dm2.
Find the number of coins, 1.5 cm is diameter and 0.2 cm thick, to be melted to form a right circular cylinder of height 10 cm and diameter 4.5 cm.
If the volumes of two cones are in the ratio 1 : 4 and their diameters are in the ratio 4 : 5, then write the ratio of their weights.
The surface area of a sphere is 616 cm2 . Find its radius.
From a solid cylinder whose height is 8 cm and radius 6 cm, a conical cavity of height 8 cm and base radius 6 cm is hollowed out. Find the volume of the remaining solid. Also, find the total surface area of the remaining solid.
The curved surface are of a cylinder is 1760 cm2 and its base radius is 14 cm. The height of the cylinder is
Assertion (A)
The curved surface area of a cone of base radius 3 cm and height 4 cm is 15π cm2.\
Reason (R)
Volume of a cone = πr2h
- Both Assertion (A) and Reason (R) are true and Reason (R) is a correct explanation of Assertion (A).
- Both Assertion (A) and Reason (R) are true but Reason (R) is not a correct explanation of Assertion (A).
- Assertion (A) is true and Reason (R) is false.
- Assertion (A) is false and Reason (R) is true.
A toy is in the form of a cone mounted on a hemisphere of common base radius 7 cm. The total height of the toy is 31 cm. Find the total surface area of the toy.
The circumference of the front wheel of a cart is 3 m long and that of the back wheel is 4 m long. What is the distance travelled by the cart, when the front wheel makes five more revolutions than the rear wheel?
