Define null point
define null point ​

In physics a null is a point in a field where the field quantity is zero as the result of two or more opposing quantities completely cancelling each other

at positions a, g kinetic energy is maximum.

at position d, potential energy is maximum.

answer: the metamorphic rocks are formed when they are exposed to high pressure and high temperatures. this happens when one of the earth's plates comes in contact with the other plate by traveling in opposite directions, straight into each other or slipping under one another. the friction that is caused by this activity results in   melting of rocks and when it cools they are known as metamorphic rocks. this process needs a controlled amount of pressure and temperature otherwise it may turn into magma.