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The diagram shows three positions of a projectile's trajectory - X, Y and Z. Position X happens to be the launch location, and the velocity vector is completely horizontal; the length of the arrow represents the magnitude of the initial horizontal velocity. The choices A - L represent horizontal and vertical components of velocity by vector arrows. The length of the arrow represents the magnitude of the velocity; the direction the arrow points represents the direction of the velocity.
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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 falls to the ground? 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 falls to the ground?
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 changes in the components of velocity change (or don't change) as the projectile travels along its path from X to Y to Z.
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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?
- 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 Y and Z that show a larger downward arrow for Z than for Y. And most importantly, take your time - minds-on time!!
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