What kind of umbrella would you use on a rainy day? Would you use an umbrella made of cotton or wool?

Nylon cloth is used in umbrella. Why?

Would you be able to burn a paper using concave mirror ?

A man is travelling at 10.8 kmph in a topless car on a rainy day. He holds an umbrella at an angle of 37^@ with the vertical to protect himself from rain which is falling vertically downwards. What is the velocity of the rain drop ?

How would you prepare biodiesel ?