Answer:
(a). The magnitude of the frictional force acting on the case is 66 N northward.
(b). The magnitude of the friction force acting on the case is 58.8 N southward.
Explanation:
Given that,
Mass of packing case = 30.0 kg
Mass of truck = 1500 kg
Coefficient of static friction = 0.30
Coefficient of kinetic friction = 0.20
Acceleration = 2.20 m/s² northward
(A). We need to calculate the force acting on the case
Using formula of force

Put the value into the formula


We need to calculate the maximum static frictional force
Using formula of frictional force

Put the value into the formula


The frictional force is greater then the force acting on the block
Then, The frictional force is 66 N northward.
(B). We need to calculate the force acting on the case
Using formula of force

Put the value into the formula


The static friction force is less then the force action on the case
We need to calculate the maximum static frictional force
Using formula of frictional force



So, The magnitude of the friction force acting on the case is 58.8 N southward.
Hence, This is the required solution.