12. In which of the positions shown in the picture, will Joshua have both potential and kinetic energy?

D. Only R

Explanation:

The Principle Of Conservation Of Mechanical Energy

In the absence of friction, the total mechanical energy is conserved. That means that

Em=U+K is constant, being U the potential energy and K the kinetic energy.

At the top of the path (point Q), Joshua is at rest but his height is at a maximum. Thus his kinetic energy is zero.

At point P, Joshua is at the minimum level (potential energy zero) and his speed is at a maximum.

At point R, Joshua has some height and some speed which means he has both types of energy.

D. Only R

a

explanation:

no diagram was provided, but i'm guessing it's the one i've attached to my answer.

here, a mechanical force turns the rod.   this generates an electric current in the coil, which powers the bulb.

conservation of mass

mass before something happens = mass afterwards