7

• The baby bouncer should not be used with babies that have a mass greater than 12kg. Suggest why.

  Spring may become permanently extended.
• In positions A and B the baby is stationary. Describe the energy transfers as the baby moves from position A to position B.

  In position A the baby has gravitational potential energy. This turns to kinetic energy and then elastic potential energy. In position B the energy is now all elastic potential energy.
• In one position the extension of the spring is 8.0 cm. The elastic potential energy stored by the spring is 4.0 J. Calculate the spring constant.

  8cm = 0.08m

  4 = 0.5 x k x 0.08^2

  k = 4 / (0.5 x 0.08^2)

  k = 1250