A boy finds that he can use a uniform plank of wood for a seesaw if he tries to balance it
2 m from the end using a tree trunk as the
pivot. If the boy sits at the end of the shorter
side, the plank will balance the boy's weight.
If the plank is 7 m long and weighs 500 N.
What is the weight of the boy? ​

The amount of heat required to change liquid water to vapor at its boiling temperature is 2256 kj/kg. the amount of heat required to change liquid mercury to its vapor state at its boiling temperature is 295 kj/kg. one kg of each substance is currently at its boiling point. how will the amount of thermal energy required to change each substance from a liquid to a gas differ?