An object is dropped from the top of a building through the air (friction is present) to the ground below. How does its kinetic energy (KE) just before striking the ground compare to its gravitational potential energy at the top of the building

An object is dropped from the top of a building through the air (friction is present) to the ground below. Kinetic energy just before striking the ground will be less than the gravitational potential energy at the top.

Explanation:

Kinetic energy is energy which the body possesses while in motion. Gravitational potential energy is one that an object has due to its position in the Gravitational field. When an object falls its gravitational potential energy is converted into kinetic energy.

When the object comes close to the ground its gravitational potential energy that has now been converted in kinetic energy will be less.

216.31 (the work done by gravity is -216.31) positive for going up.

Explanation:

We look at this question first by getting the right equation for work.

Which should be... W = F x D.

From this, we can do everything, we need the Force (F) first - the question tells us that Joe is lying on his back and moves his arms upward to raise the barbell. This means that he is countering the force of graving on the object.

What is the formula for the force of gravity on an object near the earth?

Right here --- = mg

m = the mass and...

g  =  the acceleration due to gravity which is 9.81 m/s2

Before we plug things in though, we need to convert everything to SI units,

the weight is in kg - so we're good to go there, but the length of Joe's arms are in "cm" we need m or meters. Converting 70 cm to m = .7 m.

Now, we just put it all together - (31.5kg)(9.81m/s2)(.7m) =  216.31 J or 216.31 N m.