Remember: F=-kx When the baby was at rest in the seat, the seat was 0.30m lower than without the baby.
Thus, the force of the spring pulling up must have equalled the force of gravity pulling down!

k(0.3m)=(10kg)(9.8m/s^2)

This gives, k=(98/0.3)kg/s^2

putting this into the equation from before gives:

mv^2 = (98/0.3)(0.45)^2 which can be solved for v:

v = {[(98/0.3)(0.45)^2]/(10)}^(1/2)

v = 2.6 m/s

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