Vectors and Projectiles - Mission VP9 Detailed Help

A ball is thrown upward at an angle to the horizontal. The components of the initial velocity vector are shown. Choose the letter that represents the components of the velocity vector at position Z.


 
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 Z is the location along the trajectory where the projectile has fallen back to its original height - the same height as position V.


 
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. How do the horizontal and vertical components of the velocity compare to each other at positions 2-seconds before the peak and 2-seconds after the peak? That is, when a projectile is at the same height at two different times in its trajectory (before and after the peak location), how do the components of the velocity vectors compare?
 
Once you have become certain of the answer to this question, 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 proper diagram, you are showing how the two 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.


 
An effective strategy for answering this question involves the following steps:
  • Use a knowledge of physics to decide how the horizontal and vertical components compare to each other at positions along the trajectory that are the same amount of time prior to and after the peak.
  • Decide on the direction of the vertical velocity at location Z - up or down or none at all?
  • Pick the choice of vector arrows that are consistent with the decision (above) you have made. Most important of all, take your time - minds-ontime!!


 

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