Helppp with the problem of physics

The focal length of a relaxed human eye is approximately 1.7 cm. when we focus our eyes on a close up object, we can change the refractive power of the eye by about 16 diopters. (a) does the refractive power of our eyes increase or decrease by 16 diopters when we focus closely? explain. (b) calculate the focal length of the eye when we focus closely.

If forces acting on an object are unbalanced. true or false

Where is the potential energy throughout the loading, cocking, and releasing of the trebuchet?