3) A 50 kg girl stands on a platform with wheels on a frictionless horizontal surface as shown below. The platform has a total mass of 1,000 kg and is attached to a massless spring with a force constant k equal to 1,000 N/m The girl throws a 1 kg ball with an initial velocity of 35 m/s at an angle of 30 degrees to the horizontal. a) what is the recoil velocity of the platform girl system? b) what is the elongation of the spring?