You are pushing a shopping cart. if you take items out of your cart but push at the same distance how does your work change? your work will?
a. increase because you have less to push
b. decrease because you have less to push
c. not change because distance does not change
d. can't be determined from the information given

This is a sly, sneaky question.

-- If friction is not involved, then no work is required to keep a moving shopping
cart going horizontally.  Force is only needed to speed it up, slow it down, turn
it, or lift it, but not to keep it moving on a level floor in a straight line at constant
speed.  Without friction, your work will not change:  No work was necessary to
push it before, none is needed now, and the weight of the groceries doesn't matter.

-- But if there's friction involved, (which there always is), then the whole picture
changes.  With friction present, Newton's laws of motion are out the window,
and our everyday experience applies:  It takes force to make an object move,
it takes constant force to keep a moving object moving, and a moving object
with zero net force acting on it stops moving.

In the supermarket, the loss of energy to friction depends on the weight of the
load, whether it's sliding or rolling.  Friction is not a real force, but it can very
effectively and successfully be handled like one.  It behaves as if it were a force
acting in the direction exactly opposite to the motion, with a strength that depends
on the weight that's sliding or rolling.

So if you take things out of the cart (and return them to their proper places on the
shelf please), then the weight is less, the friction is less, there is less energy lost
to friction, and you need less work to keep the cart moving the same distance as
before, at the same speed as before.

To use anything transparent