91Ó°ÊÓ

A body with a mass \(m\) slides along the surface of a trihedral prism of mass \(M\), whose upper plane is inclined at an angle \(\alpha\) to the horizontal. The prism rests on a horizontal plane having a vertical wall at the rear edge of the prism to keep it at rest. The force exerted by the base of the prism on the horizontal plane is (a) \(M g\) (b) \(m g\) (c) \(M g+m g \sin ^{2} \alpha\) (d) \(M g+m g \cos ^{2} \alpha\)

In an atom the forces acting between proton and electron are (a) nuclear (b) electromagnetic (c) gravitational (d) weak