8.9 Variation and Problem Solving

Question

The force F needed to break a board varies inversely with the length l of the board. If it takes 24 pounds of pressure to break a board 2 feet long, how many pounds of pressure will it take to break a board that is 5 feet long? Give your answer as a decimal and do not include units.

Answer 1

F = k/L^2

24 = k/2^2

24 = k/4

k = 96

F = 96/L^2

FOr L=5, F = 96/5^2 = 96/25 = 3.84 pounds per square foot