# Forces Exerted on Objects in Contact

1. Oct 23, 2012

### doug1

1. The problem statement, all variables and given/known data

Three boxes are stacked, one on top of the other. The mass of the top box is 4kg. The mass of the middle box is 3.5kg. The mass of the bottom box is 3.0kg. What is the force exerted by the middle box on each of the other boxes?

2. Relevant equations

Fg = mg

3. The attempt at a solution

Force exerted by the middle box on the upper box:

FN (normal force) = force of middle box on upper box

FN = mg = (3.5 kg + 3.0 kg) * 9.8 N/kg

FN = 63.7 N

Therefore the force of the middle box on the upper box is 63.7 N.

Force exerted by the middle box on the lower box:

Force of middle box on lower box = mg = (4.0 kg + 3.5 kg) * 9.8

Force of middle box on lower box = 73.5N

Therefore the force of the middle box on the lower box is 73.5 N.

Is this correct?

2. Oct 23, 2012

### Mesmerr

Normal force act up wards so the middle box will be acting on the top box and the bottom box will acting up on the middle box. So the middle box acts upwards on the top box with the same force as the weight of the top box.

Just remember that for any force there is an equal and opposite reaction.