You stand at the top of a cliff while your friend stands on the ground below you. You drop a ball from rest and see that it takes 1.7s for the ball to hit the ground below. Your friend then picks up the ball and throws it up to you, such that it just comes to rest in your hand. What is the speed with which your friend threw the ball

16.7m/s

Explanation:

Using v= u+ at

V = final velocity. U = initial velocity

So since the two movements are the same they will return with the same speed they went up

Then final velocity v= 0

So

0:= u +-9.8 x 1.7

U= 16.7m/s

hotter stars = bluer stars

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.