ch06-p008 - 8. In addition to the forces already shown in...

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8. In addition to the forces already shown in Fig. 6-21, a free-body diagram would include an upward normal force N F G exerted by the floor on the block, a downward mg G representing the gravitational pull exerted by Earth, and an assumed-leftward G f for the kinetic or static friction. We choose + x rightwards and + y upwards. We apply Newton’s second law to these axes: 0 N Ff m a PF m g −= +− = where F = 6.0 N and m = 2.5 kg is the mass of the block. (a) In this case, P = 8.0 N leads to F N = (2.5 kg)(9.8 m/s 2 ) – 8.0 N = 16.5 N. Using Eq. 6-1, this implies ,max 6.6 N ss N fF μ == , 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.

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