A 20.0-kg rock is dropped and hits the ground at a speed of 90.0 m/s. Calculate the rock’s gravitational potential energy before it was dropped. (Ignore the effects of friction.)

1,800 J

81,000 J

8,100 J

18,000 J

Suppose that one doll house uses the 1 inch scale, meaning that 1 inch on the doll house corresponds to 1/2 foot for life-sized objects. if the doll house is 108 inches wide, what is the width of the full-sized house that it's modeled after? in inches and feet.