Today Puzzle #578
Puzzle No. 578鈥� Monday 30 September
A father sits his two daughters on one side of a see-saw and plans to balance it with his weight on the other side. He places one daughter 2 meters from the pivot and the other 1 meter from the pivot. Knowing the father weighs 90 kg, each daughter weighs 20kg and turning moments are defined as ‘force times distance’, where should the father sit so as to balance the see-saw at the first attempt?
Today’s #PuzzleForToday has been set by Dr Geoff Evatt, Department of Mathematics, University of Manchester
Click here for the answer
66.7 centimetres from the pivot. One girls sits 2m one side of the pivot point of the see-saw. This gives a turning moment of 2m x 20kg x gravity. He places the other girl 1m from the pivot, giving a turning moment of 1m x 20kg x gravity. The combined turning moment on the girls side is thus (40 + 20) x gravity. If we label the balance position as y, which is distance from pivot towards the father, then his turning moment is ym x 90kg x gravity, which is 90y x gravity. And so, in balance, the turning moments on either side of the pivot must equal, meaning 60 x gravity = 90y x gravity. Cancelling gravity allows y to be found as 2/3 of a meter, or 66.7 cm, away from the pivot.
-
![]()
Puzzle for Today 鈥� Index
Find all of the currently available Puzzles for Today, with answers.
More fiendish brain-teasers and quizzes on 麻豆官网首页入口 Radio...
-
![]()
From autumn leaves to the magic roundabout: test yourself with our favourite quizzes.
-
![]()
We asked the intelligence agency to set our listeners a code-cracking challenge... Can you solve it?
-
![]()
Quiz: How many of these Mastermind music questions can you answer?
Here's a chance to find out whether your specialist subject on Mastermind could be the entire history of music.
-
![]()
Six conundrums to grapple with, including the Riddle of the Sphinx. Try not to forfeit your life...
