A cinder block is sitting on a platform 20m high. It weighs 79N.

A cinder block is stationary it means it only has potential energy.

Explanation:

                         Potential energy (PE) = mgh

where,

m= mass of the block

g= acceleration due to gravity

h= height of the block

Now,

                         PE= 79 × 20 J

                   or, PE = 1580 J

The energy stored by the block as potential energy is 1580 J.