8. In addition to the forces already shown in Fig. 6-21, a free-body diagram would include an upward normal force NFGexerted by the floor on the block, a downward mgGrepresenting the gravitational pull exerted by Earth, and an assumed-leftward Gffor the kinetic or static friction. We choose +xrightwards and +yupwards. We apply Newton’s second law to these axes: 0NFf maPF mg−=+−=whereF= 6.0 N and m= 2.5 kg is the mass of the block. (a) In this case, P= 8.0 N leads toFN= (2.5 kg)(9.8 m/s2) – 8.0 N = 16.5 N. Using Eq. 6-1, this implies ,max6.6 NssNfFμ==, which is larger than the 6.0 N rightward force – so the block (which was initially at rest) does not move. Putting a= 0 into the first of our equations above yields a static friction force of
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This note was uploaded on 05/17/2011 for the course PHY 2049 taught by Professor Any during the Spring '08 term at University of Florida.