Thread: eww...vectors...

here's the problem:

The magnitude and direction of two forces acting on an oject are
-70 lbs, S56[degree]E and
-50 lbs, N72[degree]E.
find the magnitude, to the nearest hundredth of a pound, and the direction angle, to the nearest tenth of a degree, of the resultant force.

i did this problem like 5 times! i keep getting different answers.
the answer in the back of the book is 108.21 lbs, S77.4[degree]E.
could someone explain it to me?

tthhhaannnk you, even for reading my post. thanks.

Hello, CONFUSED_ONE!

I assume you're familiar with trig forms for vectors.

The magnitude and direction of two forces acting on an object are:
70 lbs, S 56° E and 50 lbs, N 72° E.

Find the magnitude, to the nearest hundredth of a pound,
and the direction angle, to the nearest tenth of a degree,
of the resultant force.

Answers: 108.21 lbs, S 77.4° E

Code:

              Q
      |       *
      |     *
      |72°*
      | * 18°
    O * - - - - - - -
      | * 34°
      |56°*
      |     *
      |       *
      |         *
      |           *
                  P

The object is at .
Rewrite the bearings (angles) relative to the positive x-axis.

The forces are:

. . . . . . . and:


The resultant vector is the sum of these vectors:

. .

. .

The magnitude is: 108.21


The resultant makes an angle with the positive x-axis where:
. .

Therefore, the direction is: S 77.4° E