A 2.0 \mathrm{~kg} box is originally at rest on a horizontal surface where the coefficient of static friction between the box and the surface is \mu_{s} and the coefficient of the kinetic friction between the box and the surface is \mu_{k}=0.90 \mu_{s}. An external horizontal force of magnitude P is then applied to the box. Which of the following is a graph of the acceleration of the box a versus the external force P ?
Answer Choices
A. fma2015q4a
B. nan
C. nan
D. nan
E. fma2015q4b