3. A rock is dropped (from rest) from the top of a 60 m tall building. How far above the ground is the rock 1.2 s before it reaches the ground?
4. A mother racing her son has half the kinetic energy of the son, who has half the mass as the mother. Mother speeds up by 1.0 m/s and then has the same kinetic energy as that of the son. What are the original speeds of the mother and the son?