Exercise 7.11
Why is it easier to open the lid of a can by using a spoon as shown in Fig. ?
Not cross-checked
NCERT prints no numerical answer for this exercise, so this working has not been cross-checked against the book.
Because the spoon acts as a lever with a long effort arm and a very short load arm.
Fulcrum: the rim of the can, where the spoon rests. Load: the edge of the lid, gripped by the spoon's tip, just next to the rim. Effort: your hand pressing down at the far end of the handle.
The effort arm (fulcrum to hand) is many times the load arm (fulcrum to lid).
\(\displaystyle \text{MA} = \dfrac{\text{effort arm}}{\text{load arm}} \) (Eq. $\displaystyle 7.16$) is therefore much greater than 1.
So a small effort at the handle produces a large force on the lid, enough to prise it off — your hand moves through a large distance while the lid lifts only a little, keeping the total work the same.