What goes up but never comes down?

In four steps you need to move the word 'cold' From 'warm' by replacing one alphabet at a time such that every word formed at each step is acceptable in English Dictionary.

Three cars are driving on a track that forms a perfect circle and is wide enough that multiple cars can pass anytime. The car that is leading in the race right now is driving at 55 MPH and the car that is trailing at the last is going at 45 MPH. The car that is in the middle is somewhere between these two speeds.
Right now, you can assume that there is a distance of x miles between the leading car and the middle car and x miles between the middle car and the last car and also, x is not equal to 0 or 1.
The cars maintain their speed till the leading car catches up with the last car and then every car stops. In this scenario, do you think of any point when the distance between any two pairs will again be x miles i.e. the pairs will be x distance apart at the same time ?

A man in a car saw a Golden Door, Silver Door and a Bronze Door. What door did he open first?

Can you replace the question mark with the correct number?

Find the smallest sentence with all the English alphabet.

What is the largest amount of money that you can possess in change and still if someone asks you for a dollar, you won't be able to give?

Which fur should we be getting from the Lion?

The centre of the third figure is empty. What digit should fit inside?

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?