A1.72-kg block of soft wood is suspended by two strings from the ceiling. the wood is free to rotate in pendulum-like fashion when a force is exerted upon it. a 8.50-g bullet is fired into the wood. the bullet enters the wood at 431 m/s and exits the opposite side shortly thereafter. if the wood rises to a height of 13.8 cm, then what is the exit speed of the bullet?

= 98.21 m/s                    

Explanation:

The block has a final potential energy

U = mgh

U = (1.72)(9.8)(0.138)

    = 2.3261 J

How after of the collision the block's mechanical energy is conserved, then we can calculate the block's initial velocity

     2.3261 =

     2.3261 =

            v = 1.6446 m/s

In the collision is conserved the lineal momentum of the system then:

(1.72)(0) + (0.0085)(431) = (1.72)(1.6446) + (0.085)

3.6635 = 2.8287 + 0.0085

= 98.21 m/s                    

the correct answer is b

sleep paralysis is a parasomnia, events associated with sleep.

sleep paralysis happens when you are in the middle of waking up or falling asleep. it is the feeling of being conscious but unable to move. it definitely involves hallucinations.

i had a friend that had sleep paralysis and he told me a story one time where he was laying in bed and he couldn't move his body no matter how hard he tried and there was someone standing in the corner of his room coming towards him. he couldn't move and you can't "wake up" because you are already conscious. sometimes sleep paralysis can be triggered by frequent waking up during the night based off of multiple trips to the bathroom, or if you had ever been abused, sleep paralysis can start happening from things like that.