Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

Homework Help: Some more easy problems (Help greatly appreciated)

  1. Feb 17, 2010 #1
    1. Imagine a block is sliding down a ramp. It is possible for me to stop the block by pushing the block in towards the ramp. This should seem strange, because I am exerting a force perpendicular (normal) to the motion. Why would it be able to provide a force opposite the motion?

    2. I push a block across a horizontal tabletop with a force of 18N. If the block has a mass of 12 kg, estimate (to the nearest order of magnitude) the coefficient of friction of the table that would be necessary for the block to slide across the table with a constant speed.

    3. What direction force would be necessary to keep an object moving in uniform circular motion counterclockwise?

    Tangent to the circle counterclockwise
    Tanget to the circle clockwise
    Radially inward
    Radially outward
    No force is necessary.

    4. Explain your answer to the multiple choice question above.




    2.f(k)=u(k)n



    3.1. By increasing the normal force, you also increase the kinetic friction, which is exerted opposite the motion, and reducing acceleration.

    2. w=12 * 9.8 = 117.6 N
    n= magnitude of 117.6

    18=u(k)(117.6)
    u(k)=.15 (Order of magnitude of 10^-2 N)

    3. Radially inward

    4. You would need a centripetal net force, which would be a force perpendicular to the velocity, to keep its direction constantly changing and keep it in a circle. The force points radially inward.

    Thanks for any help guys.
     
  2. jcsd
  3. Feb 17, 2010 #2

    PhanthomJay

    User Avatar
    Science Advisor
    Homework Helper
    Gold Member

    Looks good to me!
     
  4. Feb 18, 2010 #3
    Thanks!
     
  5. Feb 23, 2010 #4
     
  6. Feb 24, 2010 #5
    Bump, anyone?
     
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook