Questions Regarding a Cat Going Up a Ramp

[mazia]

No. That is not it at all.

I guess I don't know how to do that then. :( I thought I could get there by using trig and drawing the two things as a triangle.

 

[mazia]

So am I, so that's no excuse!

Right but you also have a lot more experience doing this than me so it comes more naturally to you, and things make more sense.

 

[PeroK]

Right but you also have a lot more experience doing this than me so it comes more naturally to you, and things make more sense.

Okay, but back to the problem ...

 

[erobz]

I guess I don't know how to do that then. :( I thought I could get there by using trig and drawing the two things as a triangle.

See post 24 for an explanation of that. There is no sense in me being a parrot.

Also, probably shouldn't jump track to work-energy just yet as @PeroK notes, and get back to Newtons Second Law, and kinematics. It seems like you are having trouble there.

 

[kuruman]

Okay, but using acceleration is a valid alternative to work-energy. And, given the OP's problems, it would make sense to get a solution using acceleration to get a grip on the method.

I don't see it makes sense to completely change tack at this stage.

I completely agree. I have already expressed my thoughts on the importance of being able to add vectors correctly. My intention was not to redirect the path already taken.

I will stand aside until OP has gone down the already established path and obtained the correct answer. After that, I think OP should also obtain the same answer using work-energy considerations in which case I will butt in if necessary.

 

[mazia]

I give up for now haha. I've been working on this problem for about 4 hours and I feel like I'm not getting anywhere so I'm gonna work on something else, but I'll reply back when I can take your guys' response into consideration and try the problem again. Will update soon, thank you all for the help so far, I really appreciate you all being patient with me as this is clearly not my strong suit.

 

[kuruman]

If you replace the cat with a box being pushed up a ramp you have something fairly realistic.

Just to show that it's not at all unrealistic, here is an example of a cat being pushed down a slope (actually stairs) by another cat, no less. (Posted for comic relief and not to detract from the ongoing conversation.)

 

[erobz]

I give up for now haha. I've been working on this problem for about 4 hours and I feel like I'm not getting anywhere so I'm gonna work on something else, but I'll reply back when I can take your guys' response into consideration and try the problem again. Will update soon, thank you all for the help so far, I really appreciate you all being patient with me as this is clearly not my strong suit.

It's good to change gears for a bit, and then come back with a fresh start.

 

[mazia]

Well, my next homework problem isn't exactly a nicer distraction, so I'll just try to do this. Picking up where we left off, you guys said that theta is the angle between force and displacement. I looked at 24 again, and I re-wrote the two things as vectors (tip-to-tail, is what I learned), and using trig I got theta to be arcsin(4.860/37.5)=-7.4, but that doesn't make sense because the theta is greater than 90 on the vector thing. I'm so lost right now. Am I solving for a new theta? Or am I just using the fact that because the angle between force and displacement is greater than 90 degrees, that makes my actual theta (33) negative?

This problem has given me such a headache and I have no idea what to do here. I still can't believe this is literally just for the HINT, not even tackling the actual question yet.

 

[erobz]

Don’t worry about the work. Just go back to finding the acceleration of the cat using Newton’s second law.

 

[nasu]

I guess so. I'm a pure math person so I'm very used to just seeing numbers and doing

Adding vectors is a pure math problem.
And this is the procedure you seem to struggle with. Math is not just operations with real numbers.

 

[mazia]

Adding vectors is a pure math problem.
And this is the procedure you seem to struggle with. Math is not just operations with real numbers.

I'm aware, I didn't say I was a pure math expert, but I prefer the pure math stuff I've learned over this, is what I meant.

 

[mazia]

Don’t worry about the work. Just go back to finding the acceleration of the cat using Newton’s second law.

N2L is F=ma so my Fnet is correct then? Fx,g + Fapplied?

 

[erobz]

N2L is F=ma so my Fnet is correct then? Fx,g + Fapplied?

Which way is the person pushing? Which way is the cats weight pushing (pulling)?

 

[PeroK]

N2L is F=ma so my Fnet is correct then? Fx,g + Fapplied?

I started to Google for "forces on inclined ..." and Google suggested "... plane" and this came up:

https://www.physicsclassroom.com/class/vectors/Lesson-3/Inclined-Planes

I think you need to study this first.

 

[mazia]

I started to Google for "forces on inclined ..." and Google suggested "... plane" and this came up:

https://www.physicsclassroom.com/class/vectors/Lesson-3/Inclined-Planes

I think you need to study this first.

I've looked at many different resources on this topic before I posted here, but I'll try this one, thanks.

 

[mazia]

Which way is the person pushing? Which way is the cats weight pushing (pulling)?

They're pushing to the right so that one's positive, but since the weight is pushing down, it would be -(Fx,weight)?

 

[PeroK]

I've looked at many different resources on this topic before I posted here

Okay, but you can't have understood them.

, but I'll try this one, thanks.

The question you are trying to answer assumes you understand forces on an inclined plane. That's your first priority. You can also ask questions here if you don't understand the course material.

 

[mazia]

I've looked at many different resources on this topic before I posted here, but I'll try this one, thanks.

Okay... in one of the examples, Fnet is just equal to the force parallel to the slope, which as you mentioned, is the case here too. In that case, Fnet is 39.54?? Because... Fparallel is mg*sin(theta), so plug in the values, that's what I get.

If Fnet is 39.54, dividing that by the mass gives me an acceleration of 5.34m/s^2?

 

[mazia]

Okay, but you can't have understood them.

The question you are trying to answer assumes you understand forces on an inclined plane. That's your first priority. You can also ask questions here if you don't understand the course material.

Well I assumed I understood them because when I was following along in my lectures, the stuff the professor was explaining was very straightforward and I was able to understand it.

 

[erobz]

They're pushing to the right so that one's positive, but since the weight is pushing down, it would be -(Fx,weight)?

So long as you have defined up the slope as positive…yes. And when you say down you mean to the left…if we are talking about the component of the cats weight parallel to the slope.

 

[mazia]

Hi everyone. Thank you for your help! I ended up working through it with my friend who figured out what to do. I feel annoyed that it took me this long but I'm relieved I can move on to the next question. I appreciate everyone's patience with me! Thank you!

 

[kuruman]

That's great! Would you care to post your solution here for the benefit of others who might encounter a similar problem in the future?

 

[Steve4Physics]

Sorry to interrupt but - just in case - it may be worth highlighting a possible misunderstanding.

you guys said that theta is the angle between force and displacement. I looked at 24 again, and I re-wrote the two things as vectors (tip-to-tail, is what I learned),

Drawing vectors 'tip-to-tail' is part of a method for adding 2 vectors of the same type (e.g. 2 forces or 2 displacements).

You can't add different types of vectors this way - or any other way for that matter! E.g. you can't add a displacement and a force - it wouldn't make sense.

Apologies if that was already understood though.

 

[mazia]

That's great! Would you care to post your solution here for the benefit of others who might encounter a similar problem in the future?

Sure, I'll add it to the original post!

 

[mazia]

Sorry to interrupt but - just in case - it may be worth highlighting a possible misunderstanding.Drawing vectors 'tip-to-tail' is part of a method for adding 2 vectors of the same type (e.g. 2 forces or 2 displacements).

You can't add different types of vectors this way - or any other way for that matter! E.g. you can't add a displacement and a force - it wouldn't make sense.

Apologies if that was already understood though.

Oh I see, I didn't realize this, thank you!

 

[kuruman]

Sure, I'll add it to the original post!

Please don't edit the original post because it will be confusing to newcomers. Just post the solution at the end of the thread as if you were replying to the last message so that people can see the path that you followed to get there.