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On a seesaw with sliding seats, a child is sitting on one side and an adult on the other side. The adult weighs twice that of the child. The seesaw however is balanced. Draw a figure which depicts this situation showing the distances from the fulcrum where the child and the adult are seated.
Show Answer
For balance: weight × distance must be equal on both sides. The adult's weight is twice the child's, so the adult must sit at half the distance from the fulcrum that the child sits.
For example, if the child sits 2 m from the fulcrum, the adult sits 1 m from the fulcrum (since W × 2 = 2W × 1 ). The child sits farther; the heavier adult sits closer.
Balancing the seesaw
The lever rule
n
1
L
1
= n
2
L
2
— effort × effort arm = load × load arm
↓
The adult weighs
twice
the child
so the adult's weight is 2W and the child's is W
↓
Put it in the rule
W × L
child
= 2W × L adult
= 2W × L adult
↓
The adult must sit at
half
the child's distance from the fulcrum
