A metal block is sliding along an infinite, frictionless, horizontal plane. There are only two forces acting on the metal block: gravity and an upward force from the plane. Which of the following best describes the metal block's motion?

A.

The metal block will eventually slow down and stop.

B.

The upward force will accelerate the metal block forward.

C.

Gravity will accelerate the metal block downward.

D.

The metal block will move at the same speed forever

Acave rescue team lifts an injured spelunker directly upward and out of a sinkhole by means of a motor-driven cable. the lift is performed in three stages, each requiring a vertical distance of 11.0 m: (a) the initially stationary spelunker is accelerated to a speed of 4.80 m/s; (b) he is then lifted at the constant speed of 4.80 m/s; (c) finally he is decelerated to zero speed. how much work is done on the 78.0 kg rescue by the force lifting him during each stage

Aray of light traveling parallel to the principal axis of a concave mirror will be reflected through the mirror's

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.