PLC Activity #3
Freefall
Due: see website for due date
How to get credit for this activity
First, sign-in at the computer and sign-out when the activity is complete. Show your work and
results to a PLC tutor so they can check your work and initial the signoff sheet. Be prepared to
answer questions about the activity or your results.
Freefall times of a ping-pong and golf ball
You will need a stopwatch, ping-pong, golf ball and a 2-meter stick for this activity. Suppose two
objects (one is more massive than the other) are dropped from a 2-meter height and one
carefully measures the time these objects are in the air. Question: which object hits the ground
first – the heavier or the lighter one?
a. Setup a data table to record the time of flight for the ping-pong and golf ball.
b. Drop a ping-pong ball from a 2-meter height and carefully measure the time the ball is in the
air. Repeat 10 times and record your data in a table. Before you start taking data
measurements, practice dropping and timing so that your time measurements are fairly
uniform.
c. Repeat part (b) for the golf ball.
d. Determine the average and standard deviation (σt) of both the ping-pong and golf ball using
Excel. Setup a confidence interval of (tavg ± σt).
e. Simultaneously plot two distribution curves for the ping-pong and the golf ball on the same
axis.
 If the two curves overlap such that the confidence intervals overlap, then the ping-pong
and golf ball hit the ground at the same time.
 If the two curves overlap such that the confidence intervals do not overlap, then the pingpong and golf ball hit the ground at different times.
Does the ping-pong and golf ball hit the ground at the same time?
f. Use the kinematic equations to determine of theoretical time (tthy) for an object to hit the
ground when dropped from 2 m. Is this time consistent with the confidence interval from part
(e)?
Question 1
The four motion diagrams below show an initial point 0 and a
final point 1. A pictorial representation would define the five
symbols: x0, x1, v0x, v1x, and ax. for horizontal motion and
equivalent symbols with y for vertical motion. Determine
whether each of these quantities is positive, negative, or zero.
Give your answer by writing +, −, or 0 in the table below.
A
x 0 or y 0
x1 or y1
v 0 x or v 0 y
v1x or v1y
a x or a y
Question 2
A rock is thrown directly upward past three evenly spaced windows of equal heights.
Rank the windows according to (a) the average speed of the rock while passing them,
(b) the time the rock takes to pass them, and (c) the magnitude of the acceleration of
the rock while passing them, and (d) the change ∆v in the speed of the rock during the
passage, greatest first.
B
C
D