PHYS 2211 Module 3.5

Free Fall

3.5 Free Fall

Learning Objectives

By the end of this section, you will be able to:

• Use the kinematic equations with the variables y and g to analyze free-fall motion.
• Describe how the values of the position, velocity, and acceleration change during a free fall.
• Solve for the position, velocity, and acceleration as functions of time when an object is in a free fall.

Free Fall

Practice!

Discuss!

Consider how you would answer these questions. Then bring this to class for a group discussion.

A projectile is launched straight upward at +75.0 m/s from a height of 80.0 m, at the edge of a sheer cliff. The projectile falls, just missing the cliff and hitting the ground below.

(a) Find the maximum height of the projectile above the point of launch.

(b) Find the time it takes to hit the ground at the base of the cliff.

(c) Find its velocity at impact (include sign).

A meter stick is held vertically above your hand, with the lower end between your thumb and first finger. When your friend, who is holding the meter stick, releases it, you react by grabbing it with those two fingers. You can calculate your reaction time from the distance the meter stick falls, read directly from the point where your fingers grabbed it.

(a) Derive a relationship for your reaction time (t) in terms of this measured distance (d).

(b) You can try this at home. If you do, just share the data you collected. If you cannot do this at home, assume the distance was 17.5 cm. Based on this distance, what is the reaction time?