A 2.0 kg mass traveling at 3.0m/s strikes another 2.0kg mass traveling at -1.0m/s. They collide and have a perfectly elastic collision. If the second mass is moving at 3.0m/s after the collision,
what is the speed and direction of the first mass?

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.