A ball is thrown straight up and reaches its highest point H above the point of launch before descending. Which statement correctly describes its mechanical energies at the highest point? (Ignore air resistance.)
a) Both kinetic and potential energies are zero.
b) Kinetic energy and potential energy are equal and non-zero.
c) Kinetic energy is zero and potential energy is maximum.
d) Kinetic energy is minimum but not zero; potential energy is maximum.