What explains the fact that no machine is 100 percent efficient?

Polar bears give birth and hunt on sea ice. which of the following would polar bears survive during the melting of arctic ice? growing another layer of fur during summer migrate inland to search for different food sources staying put until the ice refreezes sticking to the usual diet of seals

Brainliesttt me asap! the below reaction can be categorized as more than one type of reaction. which reactions are these, and what are the types of reactions?

If 125 cal of heat is applied to a 60.0-g piece of copper at 25.0 ? c , what will the final temperature be? the specific heat of copper is 0.0920 cal/(g? ? c) .