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===== Example: Predicting the location of a object undergoing constant velocity motion ===== | ===== Example: Predicting the location of a object undergoing constant velocity motion ===== | ||
- | A cart is given a slight push along a near frictionless track (as shown in the video below). After the push, the cart is observed to move with a near constant velocity $\vec{v}_{cart} =\langle 1.2, 0, 0 \rangle \dfrac{m}{s}$. Determine its location after 3 seconds. | + | A cart is given a slight push along a near frictionless track (as shown in the video below). |
+ | {{ youtube> | ||
+ | |||
+ | After the push, the cart is observed to move with a near constant velocity $\vec{v}_{cart} =\langle 1.2, 0, 0 \rangle \dfrac{m}{s}$. Determine its location after 3 seconds. | ||
==== Setup ==== | ==== Setup ==== | ||
+ | |||
+ | You need to predict the location of the cart using the information provided and any information that you can collect or assume. | ||
=== Facts ==== | === Facts ==== | ||
+ | |||
+ | * The cart moves to the right. | ||
+ | * The cart's velocity is given by $\vec{v}_{cart} =\langle 1.2, 0, 0 \rangle \dfrac{m}{s}$. | ||
=== Lacking === | === Lacking === | ||
+ | |||
+ | * The initial location of the cart is not known. | ||
=== Approximations & Assumptions === | === Approximations & Assumptions === | ||
+ | |||
+ | * The interactions of the cart with its surroundings, | ||
+ | * As a result, the average and instantaneous velocity are equivalent. | ||
+ | * We will assume the initial location of the cart is $\vec{r}_{i}$. | ||
=== Representations === | === Representations === | ||
- | |||
+ | * The location of the cart can be predicted using the position update formula, $\vec{r}_f = \vec{r}_i + \vec{v}_{avg} \Delta t$ | ||
+ | * The motion of the cart is represented using the following motion diagram. | ||
+ | {{url> | ||
+ | |||
==== Solution ==== | ==== Solution ==== | ||
+ | |||
+ | We can compute the final location, | ||
+ | |||
+ | $$\vec{r}_f = \vec{r}_i + \vec{v}_{avg} \Delta t = \vec{r}_i + \vec{v}_{cart} \Delta t = \vec{r}_i + \langle 1.2, 0, 0 \rangle \dfrac{m}{s} (3 s) = \vec{r}_i + \langle 3.6, 0, 0 \rangle m$$ | ||
+ | |||
+ | You might use the video to define an origin such that the initial position of the cart is $\vec{r}_i = \langle 0.4, 1.1, 0 \rangle m$. With that new information, | ||
+ | |||
+ | $$\vec{r}_f = \vec{r}_i + \langle 3.6, 0, 0 \rangle m = \langle 0.4, 1.1, 0 \rangle m + \langle 3.6, 0, 0 \rangle m = \langle 4.0, 1.1, 0 \rangle m$$. | ||
+ | |||
+ | Notice that $y$-position of the cart remained unchanged because all the motion of the cart was in the $x$-direction. |