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A child of mass 20kg sits on a swing of length 4m and swings through a vertical height of 0.9 m as shown in the figure 2.

Determine;
i).Speed of the child when passing through the lowest point.
ii).Force exerted on the child by the seat of the swing when passing through the lowest. (KCSE 2003 paper 2 question 2(b)).

Answer Text:
i).Potential energy lost = kinetic energy gained.
#Mgh =1/2 mv^2#
2 x 10 x 0.9 = #v^2#
#V =sqrt 18# = 4.24 m/s.
ii).Force is centripetal = #(m times v times v)/r = (20 times 4.24 times 4.24)/4 = 89.9N.#