Answer:
9 and 3 N
Explanation:
Forces in the same direction sum up to produce the resultant force;
One force subtract the other will give the resultant force when they are in opposite directions;
Lets say one direction is forwards and the opposite backwards;
We have one force, let's say force A, in the forwards direction and another force, force B, acting in the same (forwards) or opposite (backwards) direction;
If B is acting in the same direction, then the resultant force (in this case) will be as follows:
A + B = 12
If B is acting in the opposite direction, then the resultant force will be as follows:
A - B = 6
Summing the two equations will allow us to solve for A:
A + B + (A - B) = 12 + 6
2A = 18
A = 9
Substitute this into either of the above equations and we can solve for B:
(9) - B = 6
B = 9 - 6
B = 3
3.13x10 to the ninth power
Answer: Either it's B. The seismic waves frequency also changed multiple times.
or
D. As the wave passed through less dense material, the speed of the wave increased.
Explanation: I'll let you choose because I'm stumped on which one it is. They both sound like they would fit perfectly with the question and I've tried doing research on it but nothing can prove either one right or wrong for me.
I know seismic waves can change frequency given the density of rock\ground it's going through.
"The propagation velocity of seismic waves depends on density and elasticity of the medium as well as the type of wave. Velocity tends to increase with depth through Earth's crust and mantle, but drops sharply going from the mantle to outer core."
However, B. also fits nicely.
"Temperature tends to lower the speed of seismic waves and pressure tends to increase the speed. Pressure increases with depth in Earth because the weight of the rocks above gets larger with increasing depth."
Nevertheless, I hope it helps.