4. Lala (60 kg) lands on the ground with a downward vertical velocity of 8.0 m/s. Her center of gravity displaces downward for 0.7 m from initial contact to complete stop. a) Calculate the change in kinetic energy (KE) from initial contact to complete stop. b) Calculate the change in potential energy (PE) of her center of gravity from initial contact to complete stop. c) Calculate the work done by the ground reaction force from initial contact to complete stop. d) Calculate the average force exerted by the ground on Lala during landing