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When you studied projectile motion, you learned that for projectile motion the x acceleration is zero and constant (which results in a constant x velocity) and the y acceleration is constant and downward toward Earth with a magnitude of 9.8 m/s². What mathematical curve describes the shape of the path of the projectile? Its shape is a parabola. It turns out that the shape of the path of any object that has constant acceleration and an initial velocity that is in a different direction than the acceleration is a parabola.

In the animation shown (position is given in meters and time is given in seconds), a space probe has engines that can fire on all four sides. Two of the engines engage at t = 2 s. Restart. The acceleration is constant and zero before the engines engage, and it is constant (but not equal to zero) after the engines engage.

1. What is the direction of the x component of the acceleration after the engines engage?
2. What is the y velocity before the engines engage?
3. After the engines engage, how is the y velocity different?
4. Now click here to view the velocity and acceleration vectors. Do they match what you predicted?

Exploration authored by Aaron Titus with support by the National Science Foundation under Grant No. DUE-9952323 and placed in the public domain.