G A2.4 - Free Fall Kinematics
Get the Formative Assessment: FA02.4.pdf
This assessment covers the following video flips:
2F. Solve displacement problems in free fall.
The Formative Assessment Solved:
Circle your answers, and label them with units. Ignore air friction and use the convention that down is negative. g = 9.8 m/s/s
1-2: An air rocket is launched vertically upward at a velocity of 28.0 m/s.
1. What total time will it be in the air? (5.71 s)
2. What is the greatest height it reaches? (40.0 m)
3-4: A rock falls from rest off a cliff that is 24.0 m tall
3. What time does it take to reach the ground? (2.21 s)
4. What is its velocity of impact? (careful of the sign) (-21.7 m/s)
5. An air rocket leaves the ground at 34.0 m/s going straight up and strikes the ceiling of the gym going 26.0 m/s. How tall is the ceiling in the gym?
(24.5 m)
Help with the Quizlette:
2.4 Quizlette – Free Fall Problems
1. Red Elk drops a rock from a 12.0 m tall cliff. What time does it take the rock to hit the water, and what is the velocity of impact with the ground. Solution
2. Steve Apt's group claimed that they jumped from a cliff that was so high it took them 2.70 s to hit the water. How high was this cliff? What was their velocity of impact with the water? Solution
3. Red Elk drops a rock from a cliff that hits the water with a downward velocity of 25.0 m/s. How high is this cliff? What time did it take the rock to hit the water after he dropped it? Solution
4. A student launches an air rocket from the ground straight upwards at a speed of 23.5 m/s. To what height does the rocket rise before going back down? What total time does the rocket spend in the air? Solution
5. A batter pops a ball straight up that rises 21.0 m above the bat, before coming back down and being caught by the catcher at the same elevation the bat hit it. What was the initial upward velocity of the ball? What total time did the ball spend in the air? Solution
6. Tom Duggan shoots a rocket into the air from the ground at some velocity. It spends 8.40 s in the air before striking the ground again. What was its launch velocity from the ground? What was its height at the top? Solution
2.4 Quizlette – Free Fall (Red Elk)
1. An air rocket is launched from the ground straight up, and on the way down is strikes a light tower that is 23.0 m tall with a downward velocity of 11.0 m/s. What was its initial upward velocity? Solution
2. An air rocket is launched straight up at 31.0 m/s. What time elapses between the launch, and the point on the way down where it has a downward velocity of 17.0 m/s? Solution
3. An air rocket is launched straight upwards at 26.0 m/s. What is its velocity at a time of 4.80 s? Solution
4. An air rocket is launched straight up with a speed of 24.0 m/s and strikes a 18.0 m tall light tower on the way down. What is the velocity of impact with the light tower? Solution
More Practice: (The Homework)
Get the handout: Worksheet-2.4-FreeFallPracticeProblems.docx
Free Fall Practice Problems for A2.4
Ignore air friction and use the convention that down is negative. g = 9.8 m/s/s
1.
a-b: A baseball is popped straight up in the air at a velocity of 42.0 m/s <Video>
a. What is the greatest height it reaches? (90.0 m)
b. What time does it spend in the air before reaching the same elevation from which it was popped up? (8.57 s)
c-d: A rock is dropped from rest from the top of a cliff and strikes the ground after 2.10 seconds. <Video>
c. What is its velocity of impact with the ground? (-20.6 m/s)
d. What is the height of the cliff? (21.6 m)
e. An air rocket is launched from the ground straight up, and on the way down is strikes a light tower that is 16.0 m tall with a downward velocity of 12.0 m/s . What was its initial upward velocity? (+21.4 m/s) <Video>
2.
a-b: A soccer ball is kicked straight up from the ground, and reaches a height of 23.0 m before coming back down. <Video>
a. What time does it spend in the air (total)? (4.33 s)
b. What was its initial upward velocity leaving the ground? (+21.2 m/s)
c-d: A golf ball is dropped from a cliff and strikes the ground with a downward velocity of 34.0 m/s. <Video>
c. How high is the cliff? (59.0 m)
d. What time did it take the ball to strike the ground? (3.47 s)
e. An air rocket is launched straight up at 36.0 m/s. What time elapses between the launch, and the point on the way down where it has a downward velocity of 21.0 m/s? (5.82 s) <Video>
3.
a-b: A steel marble is launched straight up from the ground at some velocity, and stays in the air for a total time of 8.20 s before striking the ground again. <Video>
a. What was its initial launch velocity? (+40.2 m/s)
b. To what height does the marble rise before going back down again? (82.4 m)
c-d: A hot pocket is dropped from the top of a 52.0 m tall building in Manhattan. <Video>
c. What time does it take to reach the sidewalk below? (3.26 s)
d. What is the velocity of impact with the sidewalk? (-31.9 m/s)
e. An air rocket is launched straight upwards at 27.0 m/s. What is its velocity at a time of 4.80 s? (-20.0 m/s) <Video>
4.
a-b: A giant lizard jumps straight upwards from the ground at 4.30 m/s. <Video>
a. To what height does the lizard rise before going back down again? (0.943 m)
b. What total time does the lizard spend in the air? (0.878 s)
c-d: A frozen blueberry falls from a counter top and strikes the floor with a downward velocity of 4.50 m/s. <Video>
c. What is the height of the counter top? (1.03 m)
d. What time does it take the blueberry to strike the ground? (0.459 s)
e. An air rocket is launched straight up with a speed of 31.0 m/s and strikes a 12.0 m tall light tower on the way down. What is the velocity of impact with the light tower? (-26.9 m/s) <Video>
5.
a-b: A bowling ball is launched using black powder from a well casing and goes straight up 320. m before coming back down again. <Video>
a. For what time does the bowling ball stay in the air? (16.2 s)
b. What was its initial upward velocity of launch? (+79.2 m/s)
c-d: A person falls from a bridge that is 18.0 m above the water. <Video>
c. What time does it take them to reach the water? (1.92 s)
d. What is the velocity of impact with the water? (-18.8 m/s)
e. An air rocket is launched straight up and lands on the roof of a building 3.80 s later with a downward velocity of 8.60 m/s. What was its initial velocity of launch from the ground? (+28.6 m/s) <Video>
2.4 Free Fall Kinematics Practice Problems
Instruction for this unit:
General Free Fall Problem Solving Tips:
Whiteboards:
The old Instruction for this unit:
How Far part II
Even More: From How Far III (1, 3, 4, 7, 8):
1. Helen Wheels launches a rocket in the air for a total of 7.48 seconds. What time did it spend going up? What is its initial velocity? What is its final velocity? How high did it go? What is the rocket's velocity at an elevation of 50.0 m? (Why are there two answers?)
5:53 How Far III 1 vel at 50 m
3. Freda Heitz throws a ball up from the roof of a building at a height of 21.7 m. It strikes the ground 3.78 seconds later. What is the initial velocity of the ball? With what velocity does the ball hit the ground? How high above the building does the ball go? What is the velocity and displacement 2.12 seconds after the ball was released?
3:12 How Far III 3 vel and disp at 2.12 seconds
4. Catona Hotinruff is ascending in a helicopter at a rate of 13.3 m/s. At an elevation of 47.0 m, she drops a bagel out the window of the 'copter. What time does the bagel take to reach the ground? What is its velocity of impact? How high is the helicopter when the bagel hits the ground?
1:24 How Far III 4 How high the helicopter
7. Justin Case fires an air rocket upward at 34.5 m/s from ground level. Unfortunately (for him) the rocket lands on the top of a 32.0 m tall light tower on its way down. What time is the rocket in the air? How high does the rocket go? With what velocity does it strike the tower?
2:27 How Far III 7 How high the rocket goes
8. Molly Fayad pops a softball up that ends up being caught by the catcher at the same elevation as she hit it. A spectator, using a sextant, and a range finder, determines that the ball went 63.0 m into the air at its highest point. For what total time was the ball in the air? At what times is the ball at an elevation of 42.0 m?
