Answers

  • zzz
  • Helping Hand
2014-08-13T19:46:25+08:00
**For convenience imagine the cable retracts the crate to the RIGHT 
constant rate
of 0.2m/s, a constant rate of motion means no acceleration,
   thus a = 0
-the crate is in dynamic equilibrium-

Using the formula of
net Force = ma
net Force = m(0)
net Force = 0N
Then since the net force, in this case is the Force to the right MINUS the force of Friction thus
F - f = 0
F = f

Because the crate is on a flat surface, the normal force = weight
Weight = m g
Weight = 120 * 9.81
W = 1772.2 N

First calculate the force of friction using the formula
f = Fn (friction coefficient)
f = Fn (0.24)
f = 1177.2(0.24)
f=282.528N

now use this is in the equation before
F=f
F = 282.528N

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