$3.$

A system consists of a real spring $($mass m$),$ the Earth, a person $($mass M$),$ and an inclined surface $($angle $$ relative to horizontal$)$ with friction, on which the person and spring are located.

a$.$ If the person begins at rest and then runs at constant speed up the incline, what specific energies of the system are changing?

b$.$ If the person stands still and stretches the spring horizontally using both hands, what specific energies of the system change as the spring is stretched?

c$.$ To compute the change in energy of the system if the person were to slide down the incline, what would be the external work done on the system?