Which of these proteins in mammals show only primary and secondary structures?
oxytocin
keratin
hemoglobin

The correct answer is keratin. Proteins like keratin are made up of multiple peptide chains (polypeptide); these are group of amino acids joined by peptide bonds. The sequence of amino acids in a protein is the primary structure while the specific shape in which it is folded (alpha or beta) is called the secondary structure.

When the ball is rising up, it gains kinetic energy. when the ball reaches the very top, it will have all potential energy, until it falls back down and gains it kinetic energy. finally when you catch the ball or it falls back down, it would have gained its potential energy back.