An object of mass 1.5 kg rests on a shelf where it has a gravitational potential energy of 7 joules. an object of mass 4.5 kg is placed on the same shelf. what is the gravitational potential energy of this second object?

African penguins, which inhabit the coasts of southern africa, were classified as an endangered species in 2010. two significant threats to their survival are ecosystem damage from oil spills and overfishing by humans. overfishing depletes the food supply of african penguins. the best method to reduce the threat of overfishing would be to . the risk of oil spills could be reduced by increasing the use of , which should oil consumption. if an oil spill does occur, could be used to remove the oil so the ecosystem may more quickly recover.