Question

# One dimensional motion describes the changes in the position of an object over time in terms...

One dimensional motion describes the changes in the position of an object over time in terms of its displacement, velocity, and acceleration in one direction. The motion in that direction is independent of the displacement, velocity, and acceleration associated with any of the perpendicular directions. For example, the acceleration due to gravity near the surface of the earth has a value of 9.8 m/s2, downward. This affects the vertical motion of an object but has no effect on the motion of the object in either of the horizontal directions. Thus, one-dimensional motion forms the foundation of our understanding of general motion in three dimensions.

Instructions for this activity:

For our discussion, you will address one of three slightly different versions of the case of a ball falling to the base of a 50.0 m tall building.

• Neglect air resistance.
• The magnitude of the acceleration is 9.80 m/s2.
• The eventual position of the ball is at the base of the building, 50.0 m below this initial position.
• Upward is defined as positive. Displacements, velocities and accelerations directed upwards are positive. Conversely, if directed downwards, these same quantities are negative. Thus, the base of the building is located at -50.0 m, and acceleration is -9.80 m/s2.

For the Case you are assigned, answer the following questions. Support your answer with any necessary calculations.

• How long does the ball take to reach the base of the building?
• What is the final velocity of the ball just before striking the ground?

Freefall Case 1: Near the edge of the building the ball is thrown upward with an initial velocity of 14.7 m/s, at time t = 0.00 s.

Additional question: If downward were to have been chosen as the positive direction, how would this affect the values of displacement, velocity, and acceleration given in the description of the case study? Comment on the dependence of physical results, if any, on the choice of the positive direction chosen by observers.