- #1

- 99

- 30

- Homework Statement:
- Find the equivalent force

- Relevant Equations:
- Balance of moments

Could any one please help with the following?

Three forces of magnitudes 10, 3 * sqrt(5) and 25 newtons act along lines whose vector equations are respectively:

r1 = i - 2j + k(4i + 3j) , r2 = -2i + 4j + k(2i - j) and r3 = 4i + k(7i - 24j)

A fourth force F4 is introduced which reduces the system to equilibrium.

Find F4 and the vector equation of its line of action:

I get the same answer as the book for the first part, F4 = -21i + 21j but not for the second part.

I take moments about -2i + 4j to find the y-intercept of the line of action and I am led to the equation r=-(8/21)i+k(-i+j) but the book answer is r=(22/21)i + k(-i+j).

Can anyone help confirm if it is the book or I (as I suspect) that is worng?

Thanks,

Mitch.

Three forces of magnitudes 10, 3 * sqrt(5) and 25 newtons act along lines whose vector equations are respectively:

r1 = i - 2j + k(4i + 3j) , r2 = -2i + 4j + k(2i - j) and r3 = 4i + k(7i - 24j)

A fourth force F4 is introduced which reduces the system to equilibrium.

Find F4 and the vector equation of its line of action:

I get the same answer as the book for the first part, F4 = -21i + 21j but not for the second part.

I take moments about -2i + 4j to find the y-intercept of the line of action and I am led to the equation r=-(8/21)i+k(-i+j) but the book answer is r=(22/21)i + k(-i+j).

Can anyone help confirm if it is the book or I (as I suspect) that is worng?

Thanks,

Mitch.