Question

7. There are free body diagrams in the picture. Which of the diagram(s) shows an o
force? Calculate the net force in each case also mention the direction of motion.

Answer 1

Solution :-

FBD :- A

$\begin{picture}(20,10)\put(60,30){\line(1,0){80}}\put(140,30){\line(0,1){60}}\put(60,30){\line(0,1){60}}\put(60,90){\line(1,0){80}}\put(20,60) {\vector(1,0) {40}}\put(180,60){\vector(-1,0){40}}\put(160,64){8\:N} \put(36,64){10\:N}\end{picture}$

Now Net force on A

= 10 N (Towards East ) + 8 N ( Towards West)

= 10 N ( Towards East) - 8 N ( Towards East)

= 10 - 8 N ( Towards East)

= 2 N Towards East

FBD :- B

$\begin{picture}(20,10)\put(60,30){\line(1,0){80}}\put(140,30){\line(0,1){60}}\put(60,30){\line(0,1){60}}\put(60,90){\line(1,0){80}}\put(20,60) {\vector(1,0) {40}}\put(180,60){\vector(-1,0){40}}\put(160,64){8\:N} \put(40,64){8\:N}\end{picture}$

Now Net force on B

= 8 N (Towards East ) + 8 N ( Towards West)

= 8 N ( Towards East) - 8 N ( Towards East)

= 8 - 8 N ( Towards East)

= 0 N Towards East

Or net force is Zero

FBD :- C

$\begin{picture}(20,10)\put(60,30){\line(1,0){80}}\put(140,30){\line(0,1){60}}\put(60,30){\line(0,1){60}}\put(60,90){\line(1,0){80}}\put(20,60) {\vector(1,0) {40}}\put(180,60){\vector(-1,0){40}}\put(160,64){10\:N} \put(40,64){8\:N}\end{picture}$

Now Net force on C

= 8 N (Towards East ) + 10 N ( Towards West)

= 8 N ( Towards East) - 10 N ( Towards East)

= 8 - 10 N ( Towards East)

= -2 N Towards East

Or 2 N Towards East

So Block C have Net Force = 0