My physics teacher doesn't teach--can someone help please?

Question

Three forces, A, B, and C, acting together, produce a resultant force of 10 N in the +y direction.

Force A is 10 N in the +y direction.
Force B is 10 N in the -y direction.

What is the magnitude and direction of force C?
Solve by the method of components.

(I don't even know where to begin! Any help would be appreciated!)
Thanks :)

Answer 1

With this type of physics, its best to draw a diagram. Since I cannot display my diagram I can tell you how to draw one.

Draw out your coordinate system. We'll say that the 'x' direction is horizontal and the 'y' direction is vertical.

So because FORCE A is 10 Newtons in the positive 'y' direction we need to draw a vertical line. At the bottom of the line put a big circle to indicate thats where you started. At the top of the line put an arrow to indicate that there is a FORCE of 10 Newtons acting in the POSITIVE Y direction.

Now at big circle draw another line, about equal length to the first going DOWN. Put the arrow at the very bottom. This indicates FORCE B which is providing 10 Newtons in the negative 'y' direction.

This is your diagram so far...What this means is that we have something pulling that circle UP with a force of 10 Newtons, AND we have something pulling that circle DOWN with a force of 10 Newtons.

Well because the forces are EQUAL and OPPOSITE we can write this equation.

Force A + Force B = ??
Force A = 10N
Force B = -10N

10N + (-10N) = 0 N

This means that the circle doesnt move at all. its being pulled from both ends equally, so it will not move.

Now the question states that
Force A + Force B + Force C = 10N (positive direction)

we know that

Force A + Force B = 0 N

So Force C must be 10 N (+y direction)

Make sure you write the number (10) the unit (N) and the direction (+y direction). If you don't include all three, your teacher may count it incorrect

Answer 2

Zero & Zero

Its a shame when a teacher can't even show that 10 - 10 = 0!

C is the resultant force between A and B. Both these forces act along a straight line (the + and - Y axis). Note the magnitude of the forces. Both force has a magnitude of 10. This means they are equal in force - almost. Anything acting in a + direction is pulling in the opposite of anything going in the - direction. To make a long story short, the two forces cancel each other entirely. If C = A + B, then C has a magnitude of zero and a direction of zero. Forces being directional, all zero forces have no direction.

BTW: that "N" thing stands for "Newtons". It's just thrown into the mix to confuse you.

Answer 3

Force A and B cancel each other out. (Same magnitude of 10 N, opposite directions)
C must be 10 N in the +y direction