Solving Free Fall Problems (with 5 Examples)
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- Опубликовано: 24 июл 2024
- Difficulty solving free fall problems doesn't have to be your downfall. We can help. This video springboards off of two other videos - our Describing Free Fall video and our Kinematic Equations video - to explain how kinematic equations can be used to solve free fall problems.
You can find more information that supports this video on our website.
Lesson Notes: www.physicsclassroom.com/Phys...
Slides: www.physicsclassroom.com/Phys...
Teacher Resources: www.physicsclassroom.com/Phys...
Student Action Plan includes:
The Calculator Pad: 1D-Kinematics
www.physicsclassroom.com/calc...
Concept Builder: Free Fall
www.physicsclassroom.com/Conc...
Concept Builder: Up and Down
www.physicsclassroom.com/Conc...
Tutorial on Kinematic Equations and Free Fall:
www.physicsclassroom.com/clas...
Other Videos on Kinematics topics can be found at ...
www.physicsclassroom.com/Phys...
And finally, the Home Page of our complete Physics Video Tutorial is located at ...
www.physicsclassroom.com/Phys...
Thanks for your help. Thanks so much! Really good!
It helps me a lot!!
So glad it helped. Hope you can crush that Test!
Hi! I have a question for example 5, aren't you supposed to find first the maximum height when the ball was being thrown upward? The cliff was 24m above the ground and you throw the ball upward so it means the distance should be greater than 24m? Adding the distance of the ball from the cliff and the distance from the ground to the cliff will become the maximum height for the ball.
hi may i know further how did you solve for example number 4?
Really helpful!! Thanks
Thank you so much
I would like help with bouncing objects in one dimension please just some two examples
great lesson.
Thanks for the video and I have a question.
In examples 1-4, there are 2 significant figures for g (9.8). Why did you use 3 significant figures in your final answer?
Maybe the problem takes place in Athens, where g is 9.800 N/kg to four significant figures.
Thank you for the clear explaination. However, I'm confused why you have -g for both downward (example 1&2) and upward (example 3&4) motion.
One can define the - direction to be whatever direction they wish. It's an arbitrarily assigned convention. You just must be consistent within the problem. For instance, if the initial velocity is up and you make it + (+ is designated as up), then g must be made - since it is down. If the initial velocity is down and you make it + (+ is designated as down), then g must be + because it is down.
@@PhysicsclassroomVideos Thank you. It makes sense.
I appreciate with ur effort
Hey thanks.
How did you do the algebra portion I’m confused
The big idea in this algebra is you have to perform the same math operation to each side of the = sign in an effort to get the unknown variable by itself. For instance in Ex 1 ...
Multiply both sides by 2 (gets rid of 1/2 on the right side.
Divide both sides by -9.8 (gets rid of the -9.8 on the right side.
Then square root each side (the right side now becomes t). You must do the same operations on the left side in the same order.
Hello, Why do we have d -ve when the person is on a platform and throwing up rather than down?
The ball finishes below the starting point so d is -
I have a question for example question. How did you know if the distance is positive or negative
There are a few examples here. In general your safest method is to define down as the negative direction. Then any vector that is down has a negative sign in your calculations. It is not the only way to do it but it's the way that makes the most sense to the most students.
Can you explain how in example 5 the distance is -24m?
The ball starts on the cliff and finishes on the ground ... below its starting point. So overall it fell 24 m downward. Ua a negative for downward.
Excellent lectures
Thanks.
How to find the t in a free fall problem if I only been given 4m for the height
You know d, a, and vo. Use d=vo*t + 0.5*a*t^2
Thank you for the video!
I am a bit confused though- why is gravity negative in the first two problems? Shouldn't it be positive for downward motion then negative for upwards motion such as in example three? Positive and negative signs have been giving me a lot of issues in solving free fall problems :(
In all 5 problems the same convention is used: up is + and down is -. You can actually use the opposite convention if you like as long as you are consistent. You must use your convention (mine being up is + and down is -) to translate direction info into +/- signs. So since accel'n is always down, a = negative 9.8 m/s/s. If a ball falls down (that is, finishes below its starting point), then d is negative for down. In Ex. 3, the ball starts moving up, so the v-original is a + value for up. +/- signs can be confusing; you just have to think of it as a direction. Start with a convention like up is + and down is - and start translating direction to signs. Hope that helps. Mr. H
May you help me with this example?
A stone is thrown vertically upward with a velocity of 20 m/s.
a)Find the velocity after 1sec and after 2 secs
b)How far up does it travel after 1 sec and after 2 secs
c)How long will it take to get back to the point from which it was originally thrown?
can you show your work on how you use algebra to find the correct formula for time for the first example next time?
Bro especially for #4!!
thank u very much
Glad it helped.
so acceleration is negative upwards and downwards?
Upwards and downwards are directions. When we have to enter a direction into our calculator we simply decide which direction is positive and which direction is negative. There is no rule for this. It's totally the decision of the problem solver.
Sir why did you take the distance in negative value ?
d would be the symbol for displacement. Displacement is a vector and has a direction. To communicate to the calculator the direction of displacement, I use - for down and + for up (and sometimes vice versa). What is important is that you keep track of up and down and are consistent within a problem as to down being negative (or the opposite).
@@PhysicsclassroomVideos thank you sir ..
How did you get the 9.8?
Its a value that was determined through careful experiments repeated numerous times
In the last problem the velocity should be negative because it is moving downward
The math would yield an answer of -27 m/s for final velocity. This means the velocity is 27 m/s, down. The question asks for speed. Speed is a scalar with no direction so the answer is 27 m/s.
The video doesn't seem to address this fully. Sorry
@@PhysicsclassroomVideos thanks for your reply🙏🙏🙏
why is displacement negative in question 5
The ball falls DOWN. Up is + and down is -.
Is example no. 5 is not a projectile motion?
Yep. That's a projectile problem. Why do you not think it is?
@@PhysicsclassroomVideos is that the simplest solution to solve the problem even theres no x and y component of the velocity?
None of these questions involve x-components. They all involve vertical motion only. Our 2D projectile video will be coming out in about 1 month.
Hola a la rasa del Oxford 👍
Example 5
If the ball throws upward. That's mean projectile motion. Am I wrong? The ball is moving up and down.
Projectile motion would include that motion. Yes.
@@PhysicsclassroomVideos So example 5 has a mistake, because there isn't projectile motion, but the exercise mentioned throws upward.
@@KartonDoBoZ Nope. Once thrown, it's motion is governed by free fall principles ... meaning gravity is the only influence on its motion.
@@PhysicsclassroomVideos ohh Thanks 🙂
thank you so much !!
You're welcome. Glas it helped.
oh no our table, its broken