Solving for Speed: Homework Part A

In summary, the conversation was about a physics problem involving a ball on an inclined plane. The original poster was struggling with setting up the problem and asked for help, but only provided a brief summary of their work. They were advised to show their work in detail, but instead chose to provide a long explanation of their thought process. They were then directed to post on a math forum for help, where they were able to get a better explanation. The conversation also included some snarky remarks and a warning about having a negative attitude on the forum.
  • #1
roinujo1
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Homework Statement


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Homework Equations

The Attempt at a Solution


I tried using the acceleration, ax, and the distance, 9m, to find the time. THen, since speed = d/(delta)t, I got 2.12 m/s. However, the book says that the answer is 3.00m/s. This is for part A.
 

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  • #2
It's not clear what calculations you have done. Please post your work in detail.
 
  • #3
The problem talks about a ball, at rest, going down an inclined plane with an acceleration of 0.5 m/s^2. The inclined plane is 9 meters long. Once the ball gets to the bottom it goes back up another inclined plane. which is 15 meters long, it goes to rest. The question wants to know the speed when the ball is at the bottom of the first inclined plane. So, basically, the question stated that we have an acceleration of 0.5 m/s^2 but didn't tell us the time. So, to fin the time, I divided the acceleration by 9 meters, the distance. The answer would be a decimal with a unit of 1/s^2. Then, I inverted the decimal and got 18 s^2. Finally, I sqaure rooted the answer to get 4.24 seconds. My assumption was that this was the (delta)t. Now, to find the speed at the bottom of the inclined plane, I used d/(delta)t, where d is the total distance and (delta)t is the change in time. Thus, I did 9m/4.24s and got 2.12 m/s for the speed. However, the books answer was 3.00 m/s.
 
  • #4
Yeah, I read the problem statement and such.

What I wanted to see was your calculations, not a blow-by-blow account of "I did this, and I got that, but you know, I'm thinking I needed to do this as well ..."

This is Physics Forums, and we deal with equations and calculations here.
 
  • #5
Well, I don't have a solid camera and can't take a solid picture. I explained what I did and wanted help to see what I did wrong and understand why it is this way conceptually. I'll go to a math forum. Hoefully I can get a better explanation there.

Moderator note: Removed insult.
 
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  • #6
Im pretty sure my ca;lculations are correct, but my set-up is probably wrong. I just don't see why I can't get any help in setting the problem up. I can do the math. If I had trouble with that, I wouldn't be in Differential Equations.
 
  • #7
roinujo1 said:
So, to fin the time, I divided the acceleration by 9 meters, the distance. The answer would be a decimal with a unit of 1/s^2. Then, I inverted the decimal and got 18 s^2. Finally, I sqaure rooted the answer to get 4.24 seconds.
Although you made it so the dimensions are correct, this is not a valid way of finding the time.

Call the unknown final speed "V"
In terms of V, (and the given acceleration) how long will it take to reach the bottom?
In terms of V, what is the average velocity of the ball?
If you multiply the average velocity and the time it took, what should the answer come out to be?
 
  • #8
roinujo1 said:
Well, I don't have a solid camera and can't take a solid picture. I explained what I did and wanted help to see what I did wrong and understand why it is this way conceptually. I'll go to a math forum. Hoefully I can get a better explanation there.

Writing out a verbal description of calculations almost always involves more work than just typing the equations in, even as a last resort.

Good luck with trying this approach on a math forum. They'll probably tell you the same thing I did.

And I'd watch that kind of snarky attitude of yours. It'll get you banned from most help forums, including this one.
 
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  • #9
@Nathanael Thanks for the response
I figured the problem out on the math forums, so I get how to do it now.
@SteamKing
Thanks for the advice. At least I got actual help from other who can actually explain the conceptual portion of it and how to set it up. They made perfect sense.
 
  • #10
roinujo1 said:
Im pretty sure my ca;lculations are correct, but my set-up is probably wrong. I just don't see why I can't get any help in setting the problem up. I can do the math. If I had trouble with that, I wouldn't be in Differential Equations.
Often the hardest part is setting up the equations. I gather that you posted the problem on a different site, and got some help there. We would have been more than happy to help if you had shown the work you did, rather than provide a brief summary of it. When you post a homework problem here at Physics Forums, we require that you show the work you have done. Your first post in this thread just barely qualifies for "showing the work."

Most of the homework helpers and mentors on this forum would have responded exactly the same as SteamKing did, so I am in complete agreement with him. Also, if you wish to last very long here you need to dial back your attitude... Fair warning.
 

1. How do you calculate speed?

Speed is calculated by dividing the distance traveled by the time it took to travel that distance. The formula for speed is speed = distance/time.

2. What units are used to measure speed?

Speed can be measured in a variety of units, including meters per second (m/s), kilometers per hour (km/h), miles per hour (mph), and feet per second (ft/s).

3. How is average speed different from instantaneous speed?

Average speed is the total distance traveled divided by the total time taken, while instantaneous speed is the speed at a specific moment in time. Average speed takes into account any changes in speed during the entire trip, while instantaneous speed only reflects the speed at a particular instant.

4. What are the different ways to represent speed on a graph?

Speed can be represented on a graph in various ways, such as a line graph with time on the x-axis and speed on the y-axis, a bar graph comparing different speeds, or a scatter plot showing the relationship between speed and distance.

5. How does speed affect distance and time?

Speed directly affects both distance and time. The higher the speed, the greater the distance traveled in a given amount of time. Similarly, a faster speed also means less time is needed to travel a certain distance.

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