# algebra

posted by .

the weight of a symetry ball varies directly with the cube of it's radius a ball with the radius of 2 inches weighs 5.60. find the weight of a ball with a 3 inch radius

• algebra -

weight = k r^3 , where k is a constant
when r = 2, weight = 5.6
5.6 = k(2^3)
k = 5.6/8 = .7

so weight = .7r^3
when r = 3
weight = .7(27) = 18.9

or ... just use a ratio

w/5.6 = 3^3/2^3
w = 5.6(27/8) = 18.9

## Similar Questions

1. ### math-help!

A croquet ball weighs 460 grams. Together a golf ball and a croquet ball weigh the same as ll golf balls. What does the golf bal weigh?
2. ### physics

One end of a wire is attached to a ceiling, and a solid brass ball is tied to the lower end. The tension in the wire is 160 N. What is the radius of the brass ball?
3. ### 12th grade

a ball with a r of 2inches weighs 2.40 lb.find the weight of a ball of the same material with 3 inches r
4. ### Math

A ball rolls into a corner of a room, where it touches both walls (and, obviously, the floor). A larger ball rolls into the same corner so that it touches both walls and the first, smaller ball. The small ball has a radius 1 inch. …
5. ### math

A wooden ball 7 inches in radius sinks to a depth of 10 inches in a river. Find the exposed area of the ball above the water.
6. ### geometry

find how much air is in a beach ball if the inside radius of the ball is 7 inches used pi=7 over 22 and round to the nearest hundredth of an inch.
7. ### Math

A hi-tech bowling ball is constructed from concentric spheres, kind of like a perfectly round M&M peanut. The inner sphere, of material X, has a radius of 1 inch. The middle spherical shell of material Y has a thickness of 2 inches. …
8. ### physics

a ball of weight 200 grams,is tied to the end of a cord and whirled in a horizontal circle of radius 0.6 m.if the ball makes five complete revolutions in 2 seconds,what will be the linear speed of the ball?
9. ### Physics

If you are casting a shadow of a ball on the wall, how do you make the umbra larger than the ball or is it impossible. Also, how can you make the umbra smaller than the ball or is it impossible?
10. ### physics

a ball of weight 200 grams,is tied to the end of a cord and whirled in a horizontal circle of radius 0.6 m.if the ball makes five complete revolutions in 2 seconds,what will be the linear speed of the ball?

More Similar Questions