A body is falling freely under the action of gravity alone in a vacuum. Which of the following quantities remain constant during the fall? a) kinetic energy b) potential energy c) total mechanical energy d) total linear momentum
As the body is falling freely under gravity, the potential energy decreases continuously and kinetic energy increases continuously as all the conservative forces are doing work. So, total mechanical energy (PE+KE) of the body will be constant. At point A total mechanical energy will be EA=K.E+P.E EA=21mv2+mgH As velocity will be zero at A, so its kinetic energy will be zero EA=MgH Velocity at point B will be VB=2gh So energy at point B will be EB=KE+PE EB=21m(2gh)+mg(H−h) EB=mgh+mgH−mgh EB=mgH Now velocity at point C will be VC=2gh So energy at point C will be EC=KE+PE EC=21m(2gH)+mg(0) So, total mechanical energy will remain same (if we neglect the air friction).
