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:

The cinder block is not moving so it has been storing the potential energy. We can find the potential energy of the block by using the formula as:

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.