Can you help me out? I think the answer is D. Am I correct?

Question

Trace an extended problem that involves lifting a bag of sugar up to a shelf. At first to one shelf. Then it is lifted again to a second, higher shelf. Based on the numbers that are obtained from the work calculations, which of the followig is a correct conclusion?

a) the job gets easier he higher you lift the object?

b) The weight changes as the object s lifted?

c) It is less work to lift the object all the way to its final destination in one step.

d) The amount of work isthe same whether the bag is moved all at once or in two stages, provided the total height lifted is the same in either case.

Answer 1

Answer D is correct in the ideal case only. Odim..."s answer, is also correct and well reasoned.

Answer 2

The formula for work calculations is

Work = Force x Distance

where Force = Mass x Acceleration

Assuming both shelves are at normal height i.e. a few feet off the ground and therefore subject to the effects of gravity, answers a) and b) are incorrect.

And if we assume that the acceleration is the same each time the bag is lifted, the result is only dependent on the height the sugar is raised and not the number of attempts it takes to reach that height.

So you're right, answer d) is correct.

Answer 3

Yes.  You are correct the answer is D.  Answer D is wrong, except in a world without friction and even then I believe the motion of the grains of sugar would be twice as great if moved and set down twice as once.  This motion would convert to heat energy due to collisions inside the bag.  And of course, since the bag is further away from the Earth, its WEIGHT is reduced (but its mass is the same) - but these effects are so teeny that they should be ignored.

So actually, you can make a case for any of the answers to be correct, or none.  Since the methods of moving the bag are not indicated you really can't know which is the most accurate statement.

Answer 4

D is correct.