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Mr Davis 97
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Say that I have two vectors that define a plane. How do I show that a third vector is perpendicular to this plane? Do I use the cross product somehow?
I don't see how the dot product would be used... To me, it would make sense to use it when we only need to show that one vector is perpendicular to another. But here we need to show that one vector is perpendicular to a plane (that two other vectors create).jedishrfu said:What about using the dot product?
Not how I would do it.Mr Davis 97 said:Okay, so I am specifically asking this in relation to a specific problem:
Given the vector ##\vec{A} = 3\hat{i} + 4\hat{j} -4\hat{k}##,
(1) find a unit vector ##\hat{B}## that lies in the x-y plane and is perpendicular to \vec{A}.
First, we note that ##\hat{B} = B_x \hat{i} + B_y \hat{j}##, and that ##B_x^2 + B_Y^2 = 1## since ##\hat{B}## is a unit vector. Solving this system simultaneously comes up with the solution ##\displaystyle B_x = \frac{4}{5}, B_y = -\frac{3}{5}##
Yes it would, and this is something you should do, because you have a mistake, most likely in your cross product.Mr Davis 97 said:(2) find a unit vector ##\hat{C}## that is perpendicular to both ##\vec{A}## and ##\hat{B}##.
the unit vector that is perpendicular to both ##\vec{A}## and ##\hat{B}## is ##\displaystyle \hat{C} = \pm \frac{\vec{A} \times \hat{B}}{| \vec{A} \times \hat{B} |}##. After lots of calculations, we find that ##\displaystyle \hat{c} = \frac{-12 \hat{i} - 16 \hat{j} + 7 \hat{k}}{\sqrt{449}}##
(3) show that ##\vec{A}## is perpendicular to the plane defined by ##\hat{B}## and ##\hat{C}##
So would showing that ##\vec{A} \cdot \hat{B} = 0## and ##\vec{A} \cdot \hat{C} = 0## be sufficient to show that ##\vec{A}## is perpendicular to the plane?
A vector perpendicular to a plane is a vector that is at a 90 degree angle to the plane. This means that the vector is neither parallel nor in the same direction as the plane.
A vector perpendicular to a plane is defined by taking the cross product of two vectors that lie on the plane. This cross product results in a vector that is perpendicular to both of the original vectors and therefore perpendicular to the plane as well.
Yes, a vector can be perpendicular to more than one plane. This is because a vector can be perpendicular to any plane that is perpendicular to its direction. So, if a vector is perpendicular to one plane, it will also be perpendicular to any other plane that is perpendicular to its direction.
The magnitude of a vector perpendicular to a plane can be found by taking the magnitude of the cross product of the two vectors that define the plane. This magnitude represents the length of the vector and is always positive.
A vector perpendicular to a plane is important in physics and engineering because it can represent forces or motion that are perpendicular to a surface or plane. This can be useful in calculating the effects of these forces on an object, or in designing structures that can withstand perpendicular forces without collapsing.