Mass of the man, $m=65\, kg$

Acceleration of the belt, $a=1 \,m / s ^{2}$

Coefficient of static friction, $\mu=0.2$

The net force $F$, acting on the man is given by Newton's second law of motion as:

$F_{m}=m a=65 \times 1=65\, N$

The man will continue to be stationary with respect to the conveyor belt until the net force on the man is less than or equal to the frictional force $f_{s}$, exerted by the belt, i.e., $F_{ na }^{\prime}=f_{s}$

$m a^{\prime}=\mu m g$

$\therefore a^{\prime}=0.2 \times 10=2\, m / s ^{2}$

Therefore, the maximum acceleration of the belt up to which the man can stand stationary is $2 \,m / s ^{2}$