This is a physics question: An incline is 12 meters long and makes an angle of 30 degrees with the horizontal. A box weighing 98.1 N, and...

Hello!

You are right that potential energy is calculated as The given weight 98.1 N corresponds to and is unknown.

But there are some data that make possible to find the height. It is known that "an incline is 12 meters long and makes an angle of 30 degrees with the horizontal". If we consider the triangle formed by an incline, its height and a horizontal, it will be a right triangle. And by the definition of sine, h/12 = sin(30°) = 1/2.

Therefore h = 12*(1/2) = 6 (m), and potential energy is 98.1*6 = 588.6 (J), which is the desired answer.

I have to say that potential energy may be measured off any fixed level, and the real physical sense have only a change in potential energy,