A6 kilogram concrete block is dropped from the top of a tall building. the block has fallen a distance of 55 meters and has a speed of 30 meters per second when it hits the ground. a. at the instant the block was released, what was its gravitational potential energy? b. calculate the kinetic energy of the block at the point of impact. c. how much mechanical energy was "lost" by the block as it fell? d. explain what happened to the mechanical energy that was "lost" by the block.

In an old-fashioned amusement park ride, passengers stand inside a 3.0-m-tall, 5.0-m-diameter hollow steel cylinder with their backs against the wall. the cylinder begins to rotate about a vertical axis. then the floor on which the passengers are standing suddenly drops away! if all goes well, the passengers will “stick” to the wall and not slide. clothing has a static coefficient of friction against steel in the range 0.60 to 1.0 and a kinetic coefficient in the range 0.40 to 0.70. part a what is the minimum rotational frequency, in rpm, for which the ride is safe? express your answer using two significant figures. f f = rpm