Question

7. The forces F~

1 = −ˆi + ˆj, F~

2 = ˆj, F~

3 = −2ˆi − 4ˆj and F~

4 = 2ˆi are acting at D(−1, 1),

C(1, 2), A(2, 0) and B(0, −2) respectively as shown in the Fig. 2.61. Find

a) moments of all forces about O.

b) sum of moments of all forces about O.

c) moments of all forces about A, B, C and D.​

Answer 1

Answer:

F

1

+

F

2

+

F

3

+

F

4

=(

−4

i

^

−5

j

^

+5

k

^

)+(

−5

i

^

+8

j

^

+6

k

^

)+(

−3

i

^

+4

j

^

−7

k

^

)+(

12

i

^

−3

j

^

−2

k

^

)

=4

j

^

+2

k

^

⇒ motion will be in y-z plane