# Introduction to SAT II Physics

(Darren Dugan) #1

1. A

The vector 2 A has a magnitude of 10 in the leftward direction. Subtracting B, a vector of magnitude 2 in the
rightward direction, is the same as adding a vector of magnitude 2 in the leftward direction. The resultant
vector, then, has a magnitude of 10 + 2 =12 in the leftward direction.

1. D

To subtract one vector from another, we can subtract each component individually. Subtracting the x-
components of the two vectors, we get 3 –( –1) = 4, and subtracting the y-components of the two vectors,
we get 6 – 5 = 1. The resultant vector therefore has an x-component of 4 and a y-component of 1 , so that if
its tail is at the origin of the xy-axis, its tip would be at (4,1).

1. D

The dot product of A and B is given by the formula A · B = AB cos. This increases as either A or B
increases. However, cos = 0 when = 90°, so this is not a way to maximize the dot product. Rather, to
maximize A · B one should set to 0º so cos = 1.

1. D

Let’s take a look at each answer choice in turn. Using the right-hand rule, we find that is indeed a
vector that points into the page. We know that the magnitude of is , where is the angle
between the two vectors. Since AB = 12, and since sin , we know that cannot possibly be
greater than 12. As a cross product vector, is perpendicular to both A and B. This means that it has
no component in the plane of the page. It also means that both A and B are at right angles with the cross
product vector, so neither angle is greater than or less than the other. Last, is a vector of the same
magnitude as , but it points in the opposite direction. By negating , we get a vector that is
identical to.

### Kinematics

KINEMATICS DERIVES ITS NAME FROM the Greek word for “motion,” kinema. Before we
can make any headway in physics, we have to be able to describe how bodies move. Kinematics
provides us with the language and the mathematical tools to describe motion, whether the motion
of a charging pachyderm or a charged particle. As such, it provides a foundation that will help us
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