On a 15-foot seesaw problem, if the heavier person sits 6 feet from the fulcrum, how far must the lighter sit from the fulcrum to balance?

On a 15-foot seesaw problem, if the heavier person sits 6 feet from the fulcrum, how far must the lighter sit from the fulcrum to balance?

• A. 6 feet
• B. 7 feet
• C. 8 feet
• D. 9 feet

Answer: (D)

Balancing on a seesaw depends on equal torques about the fulcrum: weight times distance on each side must match. The heavier person sits 6 feet from the fulcrum on one side. The opposite end of the 15-foot beam is 9 feet from the fulcrum (since 15 minus 6 equals 9), so if the lighter person sits at that far end, their lever arm is 9 feet. The balance condition then is the heavier’s weight times 6 equals the lighter’s weight times 9, which is possible because the lighter weighs less and is farther from the fulcrum. Therefore, the lighter must sit 9 feet from the fulcrum.

Balancing on a seesaw depends on equal torques about the fulcrum: weight times distance on each side must match. The heavier person sits 6 feet from the fulcrum on one side. The opposite end of the 15-foot beam is 9 feet from the fulcrum (since 15 minus 6 equals 9), so if the lighter person sits at that far end, their lever arm is 9 feet. The balance condition then is the heavier’s weight times 6 equals the lighter’s weight times 9, which is possible because the lighter weighs less and is farther from the fulcrum. Therefore, the lighter must sit 9 feet from the fulcrum.