What is the potential energy of a 3.15-kg object at the bottom of a well 11.8 m deep as measured from ground level? J Explain the sign of the answer.

Answer 1

Good morning.

We are dealing with gravitational potential energy here. That means we need this equation:

PE = mgΔh

We can plug in our known variables. Remember that this object is BELOW GROUND, which means it has a negative height. The ground would be zero meters.

PE = (3.15 kg) (9.81 m/s²) (-11.8 m) = -364.6377 J.

We have to adjust our answer to take account of significant figures. Here, the answer should have three significant figures because the least accurate of the three known variables (all of them, in this case) have three significant figures.

So our answer is -365 J.

The answer is negative because, mathematically, we multiplied two positive numbers and a negative number. The physics explanation is that this object would have to have energy applied to it in order to lift it out of the bottom of the well, as opposed to having energy "stored" in it (as it would if it sat above the ground).