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Physics Help, Could someone check my work test coming up soon

  1. Sep 17, 2009 #1
    1. A parent pushes a baby stroller from home to daycare along a level road with a force of 38 N directed at an angle of 30° below the horizontal. If daycare is 0.83 km from home, how much work is done by the parent?

    (38N)(cos(-30))(.83km)=27.21 J

    2. You have a 0.750 kg picture frame on a mantle 1.50 m high. How much work was required to lift the frame from the ground to the mantle?

    0.750*9.80=7.35N(1.50)=11.025 J

    3. You lower a 2.50 kg textbook (remember when textbooks used to be made out of paper instead of being digital?) from a height of 1.81 m to 1.50 m. What is its change in potential energy?

    1.81-1.50=.31
    (2.50kg)(9.80)(.31)

    =7.60 J

    Please if someone could confirm these by working them out, plz be sure of the answer before responding, Thanks so much
     
  2. jcsd
  3. Sep 17, 2009 #2

    berkeman

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    Staff: Mentor

    In 1, a Joule is a Newton meter. So check your units...

    In 2, you are loose with your one "equation". The LHS does not equal the middle, but it looks like you got the right answer anyway. You should show all terms and units on each side of your equation.

    3 looks okay.
     
  4. Sep 17, 2009 #3
    On #1 Should .83 Km be 830 meters, if that is the case will it make the question correct.

    (38N)(cos(-30))(830m)= 27309.4568 J?
     
  5. Sep 18, 2009 #4
    Need multiple opinions on these physics problems

    1. A parent pushes a baby stroller from home to daycare along a level road with a force of 38 N directed at an angle of 30° below the horizontal. If daycare is 0.83 km from home, how much work is done by the parent?

    (38N)(cos(-30))(830m)=7309.4568 J?

    2. You have a 0.750 kg picture frame on a mantle 1.50 m high. How much work was required to lift the frame from the ground to the mantle?

    0.750*9.80=7.35N(1.50)=11.025 J

    3. You lower a 2.50 kg textbook (remember when textbooks used to be made out of paper instead of being digital?) from a height of 1.81 m to 1.50 m. What is its change in potential energy?

    1.81-1.50=.31
    (2.50kg)(9.80)(.31)

    =7.60 J

    Please if someone could confirm these by working them out, plz be sure of the answer before responding, Thanks so much
     
  6. Sep 18, 2009 #5

    Hootenanny

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    Staff Emeritus
    Science Advisor
    Gold Member

    Re: Need multiple opinions on these physics problems

    The left hand side is correct, but the right hand side is wrong. You might want to check that you punched the numbers into your calculator correctly
    The orange part is correct. You should note that the blue part is not equal to the orange part, so it is incorrect to state that they are.

    Has the textbook gained, or lost potential energy?
     
  7. Sep 18, 2009 #6
    Re: Need multiple opinions on these physics problems

    are the answers correct for 2 and 3?

    On 2 what to with the blue side

    lost potential energy on 3 right?
     
  8. Sep 18, 2009 #7

    kuruman

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    Homework Helper
    Gold Member

    Re: Need multiple opinions on these physics problems

    The answer to 3 is incorrect. ΔU = mgΔh, where Δh is the change in height, i.e. final value minus initial value.
     
  9. Sep 18, 2009 #8
    Re: Need multiple opinions on these physics problems

    So should the answer be (2.50)(9.80)(-.31)=-7.595
     
  10. Sep 18, 2009 #9

    berkeman

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    Staff: Mentor

    (Two threads with the same questions merged into one...)
     
  11. Sep 19, 2009 #10
    So should the answer be (2.50)(9.80)(-.31)=-7.595 FOR #3
     
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