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Work done when pushing a cart

  1. Aug 3, 2015 #1
    1. The problem statement, all variables and given/known data
    A shopper in a supermarket pushes a cart with a
    force of 35.0 N directed at an angle of 25.08 below
    the horizontal. The force is just sufficient to balance
    various friction forces, so the cart moves at constant
    speed. (a) Find the work done by the shopper
    on the cart as she moves down a 50.0-m-long aisle.
    (b) The shopper goes down the next aisle, pushing horizontally
    and maintaining the same speed as before.
    If the friction force doesn’t change, would the shopper’s
    applied force be larger, smaller, or the same?
    (c) What about the work done on the cart by the
    shopper?

    I only don't understand (c)

    2. Relevant equations
    W = Fd

    3. The attempt at a solution
    The answer for (c) is "the same" (as the answer of (a) which is 1586N). I understand since the car travels the same distance, the work done by force should be the same as (a), but if I use W = Fd to calculate (c), it should be W = (35)(50) which is not the same as (a). So, why is that?

    Thanks!
     
  2. jcsd
  3. Aug 3, 2015 #2
    For (c), the force done on the cart is not equal to 35 anymore. The speed of the cart is maintained, but not the force. Remember that the force is no longer applied at an angle.
     
  4. Aug 3, 2015 #3

    haruspex

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    What did you answer for b?
    (Your answer to a has the wrong units.)
     
  5. Aug 3, 2015 #4
    smaller

    Ok, I get it now. Thanks!
     
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