a closed system consitts of a pendumluem that is swinging back and forth. if the pendulums gravitational potential energy decreases, what else must happen to the energy of the system.

Its gravitational potential energy must increase.

Explanation:

Conservation of Mechanical Energy

The total amount of mechanical energy, in a closed system in the absence of dissipative forces like friction or air resistance, remains constant.

This means that energy cannot disappear or appear and that potential energy can become kinetic energy or vice versa.

In a closed system like a pendulum, two types of energies are considered: Gravitational potential (U) and kinetic (K). Thus, the sum of both energies must remain constant in time.

Suppose the pendulum is at a state where U=150 J, and K=350 J. The total mechanical energy is:

M = 150 J + 350 J = 500 J

If the kinetic energy decreases to a new value, say K = 200 J, then the gravitational potential must increase to compensate for this new condition, that is: U = 300 J

So, It's gravitational potencial energy must increase

Hope it helps you I'm from ph :)

that would be b i just took the test : )

d.7.5cm is your answer