I'm working on this problem for my college physics class. It has to do with forces and friction and I want to make sure I go about this problem in the right way. I believe my teacher said that this is a really "easy" problem and something about there not being weight and it was a give-me problem but I think this is the only problem I have that I don't know how to clearly go about solving.

A 100 N force is applied to a 35 kg block that sits on a surface with friction.

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That is the problem and I have already drawn the free-body diagram.

Two questions

  1. If the coefficient of static friction is 0.37, will the crate move?

  2. If not, how much additional horizontal force is required?

  • $\begingroup$ You've got some free body diagrams, how are Newton's laws now applied? $\endgroup$ – Kyle Kanos Nov 14 '14 at 18:03
  • $\begingroup$ +1 for drawing a diagram, -1 for not writing down the equations that you know to apply in this situation. You should be able to compute the magnitude of each force; see whether the pushing force is greater than the force of friction; if it is, the thing will move; if it's not, the amount by which you are short (plus a tiny bit) is the force you need to add to get it to move. $\endgroup$ – Floris Nov 14 '14 at 18:52

The static force can be calculated using $F_f=\mu \times F_N$.

$F_N = 35kg (9.81m.s^{-2}) $ $= 343.35N$

Therefore $F_f= 0.37 \times 343.35N $ $= 127,04N$

You would therefore need an extra of at least $27.04N$ in order for the block to start moving.

Hope that helps;)

  • 1
    $\begingroup$ I'm assuming this test is being conducted on the surface of Earth $\endgroup$ – martin Nov 14 '14 at 18:22

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