11.The coefficients of static and kinetic friction for wood on wood are .5 and .3 respectively.
 If a 100 N wooden box is pushed across a horizontal wooden floor with just enough force
 to overcome the force of static friction, its acceleration is
 a) .2 m/s²
 b) .5 m/s²
 c) 2 m/s²
 d) 5 m/s²