Question

b) using free body diagrams
note: if either all the vertical forces (up and down) do not cancel each other and/or all horizontal forces do not cancel each other, then an unbalanced force exists.
example #1
free body diagram net force balanced or unbalanced? why?
example #2
free body diagram net force balanced or unbalanced? why?

Explanation:

Step1: Calculate net - force for Example #1

Net force in vertical direction $F_{net1}=F_{push}-F_{grav}$. Substituting $F_{push} = 1200N$ and $F_{grav}=800N$, we get $F_{net1}=1200 - 800=400N$.

Step2: Determine balance for Example #1

Since $F_{net1}
eq0$, the forces are unbalanced.

Step3: Calculate net - force for Example #2

Net force in vertical direction $F_{net2}=F_{norm}-F_{grav}$. Substituting $F_{norm}=50N$ and $F_{grav}=50N$, we get $F_{net2}=50 - 50 = 0N$.

Step4: Determine balance for Example #2

Since $F_{net2}=0$, the forces are balanced.

Answer:

Example #1:
Net force: $400N$
Balanced or Unbalanced? Unbalanced. WHY? There is a non - zero net vertical force.
Example #2:
Net force: $0N$
Balanced or Unbalanced? Balanced. WHY? The net vertical force is zero.