Friends tell you that on a recent trip their average velocity was +20 m/s. Is it possible that at any time during the trip their velocity was -20 m/s? Explain

Yes , it is possible .

Explanation:

Suppose they travelled from A to B , a distance of 800 m at a velocity of

40m /s and then come back on the same path covering a distance of 200 m at the rate of 20/ s .In other words their velocity in their return journey was -20m /s .

Net displacement = 600 m

Total time taken = (800 / 40) + (200 / 20)

= 20 + 10 = 30 s

Average velocity = net displacement / total time

= 600 / 30 = 20 m /s .

Hence average velocity of 20 m /s is possible .  

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.

so easy. just google the electromagnetic waves and it’ll pop up.