# SAT Subject Physics Practice Question 2: Answer and Explanation

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**Question: 2**

**2.** At time *t* = *t*_{1}, an object’s velocity is given by the vector **v**_{1} shown below.

A short time later, at *t* = *t*_{2}, the object’s velocity is the vector **v**_{2}.

If *v*_{1} and *v*_{2} have the same magnitude, which one of the following vectors best illustrates the object’s average acceleration between *t* = *t*_{1} and *t* = *t*_{2} ?

A.

B.

C.

D.

E.

**Correct Answer:** C

**Explanation:**

By definition, = ∆v / ∆*t*. We determine ∆**v** = **v**_{2} – **v**_{1} = **v**_{2} + (–**v**^{1}) geometrically as follows:

Since ∆*t* is a positive scalar, the direction of is the same as the direction of ∆**v**, which is displayed above; C is best.