If you stand at the edge of a cliff that is 75 m high and throw a rock directly up into the air with a velocity of 20 m/s, at what time w ill the rock hit the ground?

Rock will hit the ground after a time of 6.45 s

initial velocity=20 m/s

initial displacement=Yo=75m

final displacement=0

using the kinematic equation

Y= Yo+ V t+ 1/2 gt²

0=75+20 t+1/2 (-9.8)t²

-4.9t²+20 t+75=0

This is a quadratic equation in t,s we use the quadratic formula

t=

t=6.45 s

when insulating materials rub against each other, they may become electrically charged . electrons , which are negatively charged, may be 'rubbed off' one material and on to the other. the material that gains electrons becomes negatively charged. the material that loses electrons is left with a positive charge.

reserve is the answer