Question

In kickboxing, it is found that the force, f, needed to break a board, varies inversely with the length, l, of the board. If it takes 15 pounds of pressure to break a board that is 7 feet long, how many pounds of pressure will it take to break a board that is 5 feet long?

Answer 1

21 pounds is this answer for the problems

Answer 2

21 pounds

Explanation:

Given that f varies inversely with l then the equation relating them is

f =
`(k)/(l)` ← k is the constant of variation

To find k use the condition f = 15 when l = 7, then

15 =
`(k)/(7)` ( multiply both sides by 7 )

105 = k

f =
`(105)/(l)` ← equation of variation

When l = 5 , then

f =
`(105)/(5)` = 21 pounds