Q9 - On a seesaw with sliding

Last updated at September 16, 2026 by

  • 📋 Revise, Reflect, Refine, Q9 (Page 138)
    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.
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    Answer
    • For balance — Effort × Effort arm = Load × Load arm
    • Let the child's weight = W, sitting at distance d from the fulcrum.
    • Adult's weight = 2W, sitting at distance L.
      • W × d = 2W × L
      • L = d / 2
    • The adult must sit at half the distance of the child from the fulcrum.
    • GIF Watch: what are the classes of Levers Animation for "What are the classes of Levers". A short looping GIF, three or four beats, drawn in the flat classroom style of the chapter. Beat 1 — Levers can be of three classes depending upon the relative positions of effort, fulcrum and load. (Ready to Go Beyond, page 135). Label every arrow and quantity, name the direction each force or motion acts in, and hold the last frame for a moment before the loop starts again.
    • Figure description (to draw) —
      • A seesaw balanced on a fulcrum at the centre.
      • Child on the left at distance d (e.g. 2 m) from the fulcrum.
      • Adult on the right at distance d/2 (e.g. 1 m) from the fulcrum.
      • Label — child weight W at 2 m, adult weight 2W at 1 m. W × 2 = 2W × 1 ✓ balanced.
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