Two-DimensionalMotionwithUniformAcceleration

　　If we break this motion into x- and y-components, the motion becomes easy to understand. In the y direction, the ball is thrown upward with an initial velocity of　and experiences a constant downward acceleration of g = –9.8 m/s2. This is exactly the kind of motion we examined in the previous section: if we ignore the x-component, the motion of a projectile is identical to the motion of an object thrown directly up in the air.　　In the x direction, the ball is thrown forward with an initial velocity of　and there is no acceleration acting in the x direction to change this velocity. We have a very simple situation where　and　is constant.　　SAT II Physics will probably not expect you to do much calculating in questions dealing with projectile motion. Most likely, it will ask about the relative velocity of the projectile at different points in its trajectory. We can calculate the x- and y-components separately and then combine them to find the velocity of the projectile at any given point:　　Because　is constant, the speed will be 美国GREater or lesser depending on the magnitude of . To determine where the speed is least or 美国GREatest, we follow the same method as we would with the one-dimensional example we had in the previous section. That means that the speed of the projectile in the figure above is at its 美国GREatest at position F, and at its least at position C. We also know that the speed is equal at position B and position D, and at position A and position E.　　The key with two-dimensional motion is to remember that you are not dealing with one complex equation of motion, but rather with two simple equations.

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