(ii) a 20.0-kg box rests on a table. (a) what is the weight of the box and the normal force acting on it? (b) a 10.0-kg box is placed on top of the 20.0-kg box, as shown in fig. 4–43. determine the normal force that the table exerts on the 20.0-kg box and the normal force that the 20.0-kg box exerts on the 10.0-kg box.

The normal force acting on the body is equal to its weight, hence;

N = W = 196N

The normal force that the 20.0-kg box exerts on the 10.0-kg box is 98N

The formula for calculating the weight of an object is expressed as:

W = mg

m is the mass of the object

g is the acceleration due to gravity.

Given the following parameters

Mass of the box = 20.0kg

a) The weight of the box = 20 * 9.8

Weight of the box = 196N

Hence the weight of the  box is 196N

Note that the normal force acting on the body is equal to its weight, hence;

N = W = 196N

b) if a 10.0-kg box is placed on top of the 20.0-kg box, the total mass will be;

M = 10 + 20 = 30kg

total weight = 30 * 9.8

Total weight = 294N

Since the normal force is equal to the weight, hence W = N = 294N

Weight of the 10kg box = 10 * 9.8 = 98N

Since the 10kg box is on top of the 20kg box, hence the normal force that the 20.0-kg box exerts on the 10.0-kg box is 98N

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*Fig is Attached with answer*

(a)   Weight = Normal Force = 196.2 N

(b)   Normal force table on 20 kg box = 294.3 N

       Normal force 20 kg box on 10 kg box = 98.1 N

Explanation:

(a)   Mass = m = 20 kg                           g = 9.81 m/s²

      Weight = w = mg

                      w = 20 × 9.81

                      w = 196.2 N

As the box rests on the table so, normal force (NF) must be equal to the weight of the box.

                    NF = w = 196.2 N

(b)

m₁ = 20 kg                      m₂ = 10 kg

total mass = M = 30 kg

Total Weight = W = Mg  

                             = 30 × 9.81

                             = 294.3 N

As both the boxes rest on the table so, normal force (NF) must be equal to the total weight of the boxes.

                          NF = W = 294.3 N

Weight of 10 kg box = 10 × 9.81 = 98.1 N

As the 10 kg box is placed on the top of 20 kg box, So 20 kg box must exert a normal force that is equal to the weight of 10 kg box.

              Normal Force = Weight of 10 kg box = 98.1 N

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there are no contact forces mentioned on the list of choices that you've provided.