What is the word or phrase?

What is the below Rebus indicate?

If you drop a 15 kg iron bar and a 5 kg bag of cotton from a height of 50 meters which will reach the ground first?

A network of 20 x 10 squares is given to you.

Can you calculate how many unique squares and rectangles can be formed combining two or more individual squares ?

Take away the whole and some still remain. What is it?

A man hijacks an aeroplane transporting both passengers(8 of them) and valuable cargo. After taking the cargo, the man demands nine parachutes, puts one of them on, and jumps, leaving the other eight behind. Why did he want eight?

I cannot talk, but I always reply when spoken to. What am I?

As easy as you can get into me, it is as hard to get out of me.

Do you know what I am?

I know a ten-letter word in the English language which can be typed using only the top rows of the computer keyboard.

People put me on the table and cut me but do not eat me. What am I?