Homework Questions?
Free Fall Last new topic that will be on the Midterm
Do now: Calculate acceleration due to gravity on earth
Announcements 3.03 is due Friday
Free Fall Introduction: Doc Shuster (AP Physics) https://www.youtube.com/watch?v=du_c6sifjn8
Key points Free Fall occurs whenever the only thing acting on an object is gravity (neglect air resistance) Acceleration on earth is equal to g ( baby g ), which is called gravitational acceleration and is equal to 9.8 m/s/s Acceleration is always downward on earth because gravity always points downward on earth!!!!
Check for Understanding A person throws a ball straight upward. 1. What is the acceleration at the very top of its trajectory? 2. What is its velocity at the very top of its trajectory?
Check for Understanding A person throws a ball straight upward. 1. What is the acceleration at the very top of its trajectory? Acceleration = g = 9.8 m/s/s downward ALWAYS! 2. What is its velocity at the very top of its trajectory? Velocity at the peak is 0 m/s because it stops for a moment before falling
Vocabulary for Word Problems Thrown up implies that the object reached a final velocity of zero at the top of the trajectory Dropped implies that the initial velocity of the object is 0 m/s (dropped as opposed to thrown downward) Acceleration on earth is always g unless otherwise noted Maximum height is talking about (vertical) distance
Work Time The same exact kinematic equations apply to these new problems but now we have more things that are implied Note: You do not need to use all the information given to solve a problem. If you can solve the problem using less information than what was given, that is perfectly fine! (You do not have to use all the variables)
Example 1. A 1.0-kilogram ball is dropped from the roof of a building 40 meters tall. What is the approximate time of fall? Answer: 2.85 seconds
When an object is traveling upward, the acceleration must be -9.8m/s/s. Otherwise, it is okay to use 9.8 m/s/s
Level 1 1. An astronaut drops a hammer from 2.0 meters above the surface of the moon. If the acceleration due to gravity on the moon is 1.62 m/s2, how long will it take for the hammer to fall to the Moon s surface? 2. A ball is thrown straight downward with a speed of 0.50 meter per second from a height of 4.0 meters. What is the speed of the ball 0.70 second after it is released? 3. How far will a brick starting from rest fall freely in 3.0 seconds? 4. A 1.0-kilogram ball is dropped from the roof of a building 40 meters tall. What is the approximate time of fall?
Level 1 1. An astronaut drops a hammer from 2.0 meters above the surface of the moon. If the acceleration due to gravity on the moon is 1.62 m/s2, how long will it take for the hammer to fall to the Moon s surface? Answer: 1.6 seconds 2. A ball is thrown straight downward with a speed of 0.50 meter per second from a height of 4.0 meters. What is the speed of the ball 0.70 second after it is released? Answer: 7.4 m/s 3. How far will a brick starting from rest fall freely in 3.0 seconds? Answer: 44 m 4. A 1.0-kilogram ball is dropped from the roof of a building 40 meters tall. What is the approximate time of fall? Answer: 2.9 seconds
Level 2 1.A rock falls from rest off a high cliff. How far has the rock fallen when its speed is 39.2 meters per second? 2.An astronaut standing on a platform on the Moon drops a hammer. If the hammer falls 6.0 meters vertically in 2.7 seconds, what is its acceleration? 3.An object is dropped from rest and falls freely 20 meters to Earth. When is the speed of the object 9.8 meters per second?
Level 2 1.A rock falls from rest off a high cliff. How far has the rock fallen when its speed is 39.2 meters per second? Answer: 78.3 meters 2.An astronaut standing on a platform on the Moon drops a hammer. If the hammer falls 6.0 meters vertically in 2.7 seconds, what is its acceleration? Answer: 1.6 m/s 2 3.An object is dropped from rest and falls freely 20 meters to Earth. When is the speed of the object 9.8 meters per second Answer: 1 Second