Given that

Mass of the stationary man, m = 65 kg

Acceleration of the conveyor belt a = 1 m/s^2

Coefficient of the static friction \mu = 0.2

Acceleration due to gravity a = 9.8 m/s^2

Normal force is balanced by the weight of the man(mg)

N = mg

There is only one force acting on the man, and it is caused by the belt's acceleration.

F_{net} = F

Step 1: Calculating the net force acting on the man

According to the newton's second law of motion

Force, F = ma

F_{net} = ma

F_{net} = 65 kg * 1 m/s^2 = 65 N

Net force acting on the man = 65 N

Step 2: Find the maximum belt acceleration at which a man can remain stationary F_s = \mu N = \mu mg

The man will remain motionless in respect to the conveyor belt until his net force is less than or equal to the belt's frictional force,( F_s ). F_s = \mu N = \mu mg

F_{net} = F_s

ma = \mu mg

a = \mu g

a = 0.2 * 9.8 m/s^2

a = 1.96 m/s^2

Hence, the maximum belt acceleration at which a man can remain stationary a = 1.96 m/s^2