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The diagram shows five positions of a projectile's trajectory. Position V happens to be the launch location. Since it is an angled-launched projectile, there is both a horizontal and vertical velocity. The length of the arrows are representative of the magnitude of the initial horizontal and vertical velocity. The choices A - R represent possible horizontal and vertical components of velocity by vector arrows. The length of the arrows represent the magnitude of the velocity; the direction the arrows point represent the direction of the velocity. Positions W and Y are positions along the trajectory that are at the same height. Position W might be a position 1-second prior to the peak of the trajectory and position Y would be 1-second after the peak. Recognizing this truth will be important to answering this question correctly.
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To be successful on this question, you will have to give much thought to what you know about the velocity of a projectile and apply it to the vector diagram that is shown. Does the horizontal velocity of a projectile change or stay the same? If the horizontal velocity changes, does it increase or decrease as the projectile travels along its path? Does the vertical velocity of a projectile change or stay the same? If the vertical velocity changes, does it increase or decrease as the projectile rises towards its peak? How does the vertical velocity change (if at all) as it falls from its peak? And finally, how do the components of the velocity compare to each other at positions 1-second before the peak and 1-second after the peak?
Once you have become certain of the answers to these questions, then you will have to search for a diagram that shows the proper direction and the relative size of these two vectors. In picking the two diagrams, you are showing how the components of velocity change (or don't change) as the projectile travels along its path from V to W. And you are showing how the components of velocity compare to each other at two locations that are the same amount of time prior to and after the peak of the trajectory.
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An effective strategy for answering this question involves the following steps:
- Use a knowledge of physics to decide how the horizontal and the vertical velocity will change during the course of the trajectory - do they increase, decrease, or stay the same? Also decide on how the components compare to each other at positions along the trajectory that are 1-second before and 1-second after the peak.
- Decide on the direction of the vertical velocity at the various locations - up or down or none at all?
- Pick the choice of vector arrows that are consistent with the decisions (above) you have made. If you have decided that the vertical velocity increases and is upward, then pick a set of arrows for position W that shows a larger upward arrow for W than that given at V. And pick the proper arrows for position Y that reflect what you know about the relative magnitude and direction of the velocity components compared to position W.
- Most important of all, take your time - minds-on time!!
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