Why do scientists believe that dark matter exists even though it cannot be seen?

What type of nuclear decay causes the atomic number of an element to increase by 1?

If the force applied to an object remains constant, is more power needed for the object to move faster ? explain

Which of these is not a possible type of energy transformation? a. electrical energy into light energy b. sound energy into nuclear energy c. potential energy into kinetic energy d. kinetic energy into mechanical energy