Why does the top of a liquid usually have a flat surface

To do work, this truck uses energy stored in chemical fuel and an electrical battery. how much total energy does this truck put out?

What happens when you slowly pulled the carboard?

Asynthetic fiber used in manufacturing carpet has tensile strength that is normally distributed with mean 75.5 psi and standard deviation 3.5 psi. how is the standard deviation of the sample mean changed when the sample size is increased from n equals 8 to n equals 47