Part A.)Six boxes held at rest against identical walls. Rank the boxes on the basis of the magnitude of the normal force acting on them.

Rank from largest to smallest. To rank items as equivalent, overlap them.

1) 130N--->7kg

2) 150N--->1kg

3) 150N--->7kg

4) 120N--->3kg

5) 140N--->5kg

6) 140N--->3kg

(Since the boxes are at rest, Newton's 2nd law dictates that the horizontal forces on each box must add up to zero. You can use this information to determine the normal forces. If two boxes are both pushed against the wall by the same force, then they should experience the same normal force.)

Part B.) Rank the boxes on the basis of the frictional force acting on them.

Rank from largest to smallest. To rank items as equivalent, overlap them.

1) 130N--->7kg

2) 150N--->1kg

3) 150N--->7kg

4) 120N--->3kg

5) 140N--->5kg

6) 140N--->3kg

Explanation:

When a body is held against a vertical wall , to keep them in balanced position , normal force is applied on their surface . this force creates normal reaction which acts against the normal force and it is equal to the normal force as per newton's third law . Ultimately friction force is created which is proportional to normal force and it acts in vertically upward direction . It prevents the body from falling down .

Hence normal force = reaction force .

From second law also net force is zero , so if  normal force is N and reaction force is R

R - N = mass x acceleration = mass x 0 = 0

R = N .

Ranking normal force from  highest  to smallest

150 N , 130 N , 120 N

B )

Frictional force is equal to the weight of the body because the body is held at rest .

Ranking of frictional force form largest to smallest

7 kg , 5 kg , 3 kg , 1 kg .

Here frictional force is irrespective of the normal force acting on the body  because frictional force adjusts itself so that it becomes equal to weight in all cases here because it always balances the weight of the body .

f=ma newton's second law 7x8=56n

answer: 2×10^-2kg

explanation: density= mass per volume

vol=mass/density

converting to s.i units we have;

3÷1000kg = 0.003

1.5÷100m = 0.15

0.003/0.15 = 0.02kg