In which one of the following circumstances could mechanicalenergy not possibly be conserved, even if friction and airresistance are absent? why? a) a car moves up a hill, its velocity continually decreasingalong the way b) a car moves down a hill, its velocity continuallyincreasing along the way c) a car moves along level ground at a constant velocity d) a car moves up a hill at a constant velocity In which one of the following circumstances could mechanicalenergy not possibly be conserved, even if friction and airresistance are absent? why? a) a car moves up a hill, its velocity continually decreasingalong the way b) a car moves down a hill, its velocity continuallyincreasing along the way c) a car moves along level ground at a constant velocity d) a car moves up a hill at a constant velocity