What brings you down but never up?

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?

Find the next number in the series?
2, 12, 36, 80, 150, 252, 392, _ ?

Accidentally, two trains are running in the opposite direction and enter a tunnel that is 200 miles long. A supersonic bird that has fled the lab and taken shelter in the tunnel starts flying from one train towards the other at a speed of 1000 mph. As soon as it reaches the second train, he starts flying back to avoid collision and meets the first train again at the other end. The bird keeps flying to and fro till the trains collide with each other.

What is the total distance that the supersonic bird has traveled till the trains collided?

There are are five things wrong with this sentence; only geniuses will be able to to spot all of the mitstakes

Replace the question mark with the correct number in below Picture:

If you had a pizza with crust thickness 'a' and radius 'z', what's the volume of the pizza?

Three doctors said that Bill was their brother. Bill says he has no brothers. How many brothers does Bill actually have?

It has five wheels, though often think four, You cannot use it without that one more, You can put things in it, you can strap things on top, You can't find it in the market, but you can still go shop. What is it?

An office is divided into 8 cubicles. How many of the cubicles are painted if only 1/8 of the cubicles are painted?