EF 151
Lab 1.5
Spring 2017
Lab 1.5 Free Fall, Constant Acceleration
Objectives
- Continue to work constant acceleration problems, including those with freely falling objects.
Task 1
Answer the following concept questions.
1. You and your dog go for a walk to the park. On the way, your dog takes many side trips to chase squirrels or
examine fire hydrants. When you arrive at the park, do you and your dog have the same displacement? Have
you and your dog traveled the same distance?
2. When throwing a ball straight up, which of the
following is true about its velocity, v, and its
acceleration, a, at the highest point in its path?
A) both v = 0 and a = 0
B) v ≠ 0, but a = 0
C) v = 0, but a ≠ 0
D) both v ≠ 0 and a ≠ 0
E) not really sure
4. You throw a ball upward with an initial speed of 10
m/s. Assuming that there is no air resistance, what is
its speed when it returns to you?
A) more than 10 m/s
B) 10 m/s
C) less than 10 m/s
D) zero
E) need more information
3. Alice and Bill are at the top of a building. Alice
throws her ball downward. Bill simply drops his ball.
Which ball has the greater acceleration just after
release?
A) Alice’s ball
B) it depends on how hard the ball was thrown
C) neither -- they both have the same acceleration
D) Bill’s ball
5. Alice and Bill are at the top of a cliff of height H.
Both throw a ball with initial speed v0, Alice straight
down and Bill straight up. The speeds of the balls
when they hit the ground are vA and vB. If there is no
air resistance, which is true?
A) vA < vB
B) vA = vB
C) vA > vB
D) impossible to tell
Task 2. Constant Acceleration
Dean Wayne Davis goes out for a ride on his Uno. He starts from rest and
accelerates at 2 ft/s2 for 20 seconds. He then hits a stiff head wind and his
acceleration is -0.5ft/s2 for the next 375 ft. Finally, he covers the next 600 ft in 12
seconds, accelerating at a uniform rate. Determine the total distance the esteemed
Dean covers, the total time he takes, and his final velocity.
Hint: This is three constant acceleration problems. The key is to keep organized.
As discussed in the last lab, a table can be useful to keep organized. Note that the
final position and velocity for Leg A are the initial position and velocity for Leg B.
Leg
s1 (ft)
A
0
s2 (ft)
v1 (ft/s)
v2 (ft/s)
a (ft/s2)
t (s)
2
20
B
C
Total
1
EF 151
Lab 1.5
Spring 2017
Task 3. Tennis Ball
1. A tennis ball is dropped from a height of 5 ft. Neglecting air resistance, calculate the time it takes for the
tennis ball to hit the floor.
2. A tennis ball is thrown up in the air at a starting point of 5 ft above the ground. It takes 1.1 seconds for the
tennis ball to hit the floor. How high was the tennis ball thrown?
Using a tennis ball and the Video Physics app on your iPad, film Situation 1 and Situation 2.
Using the instructions provided, plot the path of the ball for each video. Using the graphs generated, answer the
following questions:
Situation 1
1. How long did it take the tennis ball to hit the ground?
2. How would you describe the y-velocity vs. time graph (for example: constant, linear, parabolic)?
3. What is the magnitude of the acceleration of the ball?
Situation 2
1. How high was the tennis ball thrown?
2. Based on the position and velocity graphs (y-direction) what is the velocity of the ball when it reaches its
maximum height?
3. What happens to the acceleration when the ball reaches its maximum height?
2