Question

What is the gravitational potential energy of a 61.2-kg person standing on the roof of a 10-story building relative to the tenth floor, sixth floor, and first floor? Each story is 2.50 m high.

Answer 1

Relative to the tenth floor - zero; relative to the sixth floor - 6000 J and relative to the first floor (which is ground level I assume?) - 15000 J.

Explanation:

Let me get you started. The relation we want is

U = m g h

U is the change in PE, m is the mass raised through a distance h.

So, given m = 61.2 kg, each 1 m rise is an increase of (61.2)(9.8) = 600 J.

Likewise, each floor (2.5 m) represents a change in PE of 1500 J for this mass.

Now, all you have to do is count the number of floors ascended in reaching the tenth floor from each starting point, and you get the answers I proved.