2. a 200-kg boulder has 39,200 joules of gravitational potential energy. what height is it at? 3. a 1-kg model airplane has 12.5 joules of kinetic energy and 98 joules of gravitational potential energy. what is its speed? what is its height?

As per the first question we have to calculate the height at which the boulder is present.

we have been given the mass of the boulder [m] as 200 kg.

The gravitational potential energy is given as 39,000 Joule.

The gravitational potential energy at a height ' h'  from the surface earth is given as P.E= mass×height×acceleration due to gravity

The value of g=9.8 m/s^2

   Hence height [h]

                              =

                              =19.8979 metre

As per the second question we have to calculate the sped and height of the model airplane.

the mass of model airplane is 1 kg

The kinetic energy [K.E] of the airplane is 12.5 joule

we have K.E

                K.E

                      v=5 m/s

Again we have to calculate the height [h]

The potential energy is given as 98 Joule.

we know that P.E= mgh

                        tex]h=\frac{P.E}{mg}[/tex]  

                       =

                       =10 metre

the answer is a. at the equator