Physics - NLM Question with Solution | TestHub

Maximum static friction on A and B:
$f_{s,A}^{\max }=0.4(0.5)(10)=2\mathrm{N}$
$f_{s,B}^{\max }=0.2(0.5)(10)=1\mathrm{N}$
Together they remain at rest until the applied force reaches 3 N:
$F(t)=t\mathrm{N},t=3\mathrm{s}$
Thus from 0 to 3 s, displacement is zero; friction and tension do zero work.
A, B and C follow.
After sliding begins, total kinetic friction is 2 N:
$a=\frac{t-2}{1}=t-2$
Starting from rest at 3 s, integrate the acceleration:
$$v(10)={\int }_3^{10}(t-2)\mathrm{d}t$$
$$v(10)={\left[\frac{t^2}{2}-2t\right]}_3^{10}=31.5m/s$$
This is not 27.5 m/s, so D is false.