A 2.1 kg ball is attached to a ceiling by a string. The distance from the ceiling to the center of the ball is 1.11 m, and the height of the room is 3.00 m.

Question

(a) What is the gravitational potential energy associated with the ball relative to the ceiling?

 

(b) What is the gravitational potential energy associated with the ball relative to the floor?

 

(c) What is the gravitational potential energy associated with the ball relative to a point at the same elevation as the ball?

Answer 1

Gravitational potential energy is given by PE = mass x gravitational constant x distance from the reference level. If the mass is higher than the reference level, the PE is positive. If lower than the reference, the PE is negative. If mass is at reference level, the PE is zero.

(a) The mass is below the reference level and is located 1.11 m below the ceiling. The PE = - 2.1 kg x 9.8 ms^-2 x 1.11 m = - 22.8 joules.

(b) PE = 2.1 kg x 9.8 ms^-2 x (3.00 - 1.11 m) = 38.9 j

(c) PE = 0

check my math.