Find the PE of a 25-kg object 1.67 m above the surface of the National Mall in Washington,DC.Take the surface of Tiananmen Square to be zero potential.Possibly useful information Beijing elevation: 43 m above sea level.
National Mall elevation: 10 m above sea level
Radius of the Earth: 6.38 * 10⁶ m.
Assume that DC and Beijing are directly opposite each other for this problem.

Question

Quizplus · Accepted Answer

The formula for calculating gravitational potential energy is PE = mgh, where m is the mass (25 kg), g is the acceleration due to gravity (9.81 m/s^2), and h is the height above the zero point (in this case, the surface of Tiananmen Square which is at 43-10=33 m above the National Mall). Therefore, h = 1.67 + 33 = 34.67 m.

PE = (25 kg)(9.81 m/s^2)(34.67 m) = 8547.5 J

However, since we are asked for the PE relative to the National Mall, we need to subtract the PE of the object at the National Mall height.

PE at National Mall height = (25 kg)(9.81 m/s^2)(10 m) = 2452.5 J

PE = 8547.5 J - 2452.5 J = 6095 J

Since the object is above the zero point, the PE is positive. The closest choice is B, -7700 J, which is the closest to but still less than our calculated value of 6095 J.

Find the PE of a 25-Kg Object 1