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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. Position W represents a position along the trajectory as the projectile is still rising upward and position X represents the very peak of the trajectory.
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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 rises towards the peak of its trajectory? 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 the peak of its trajectory? Is there anything unique about these velocity components for the peak position?
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 to X (the peak).
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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 while a projectile rises towards the peak - do they increase, decrease, or stay the same?
- 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 two decisions (above) you have made. If you have decided that the vertical velocity increases and is downward, then pick a set of arrows for positions W and X that show a larger downward arrow for X than for W and a larger downward arrow for W compared to that shown for V.
- Most importantly, take your time - minds-on time!!
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