# Search results

1. ### 4 Momentum Questions

My Comment Regarding Your Answer to 'question7.jpg' Actually, you can correctly solve your problem that way. Unfortunately, you made a mistake in the quoted text below. Well, you have to obtain the F_{average} of the braking force depicted in the graph. It is easy to obtain it as follows...
2. ### 4 Momentum Questions

Answer to 'question7.jpg' Using law of conservation of enery, treating the cyclist, the cycle and the ground as an isolated system, and assuming that the ground is flat and the brake transfers all of the kinetic energy into thermal energy, we can solve the problem presented in 'question7.jpg'...
3. ### Work and ramps

Hi Ho! I've just discussed this problem with an assistant of school's physics laboratory and it turns out that your answer on choosing x=90° is correct. In fact, when you use a ramp, you'll get an angle that maximizes your Fpush. Thank you. PS: What's wrong with the LaTex generator? It can't...
4. ### Work and ramps

Mentor, we need help! Mmm... OK! :smile: Let's assume that \mu = \frac{1}{2}. So, Fpush( \arctan ( \frac{1}{ \frac{1}{2}}))=Fg( \sin ( \arctan ( \frac{1}{ \frac{1}{2}}))+( \frac{1}{2}) \cos ( \arctan ( \frac{1}{ \frac{1}{2}}))) Fpush( \frac{1}{2})=1.12 Fg If we use your argument that x...
5. ### Work and ramps

Mmm... I think... Hi Ho! :smile: The correct answer is \tan(x)=\frac{1}{\mu}. You're correct. Those are synonymous with varying the ramp's angle. Well, don't go straight to that point. Using calculus to guide us to a good common sense will prove that your reasoning above is not...
6. ### Linear Algebra - Linear Transformation

Hi Ho! ^_^ I stuck when doing David C. Lay's Linear Algebra in Exercise 1.8 about Linear Transformation I'm asked to determine whether these statements are correct. Statement 1: A linear transformation is a special type of function. Statement 2: The superposition principle is a physical...
7. ### A system with varying mass - a rocket

Hi Ho! ^_^ Although I'm still confused, thank you very much for all of your helps! ^^v I really appreciate it! ^^
8. ### A system with varying mass - a rocket

Mmmm... yup! I know exactly that dM is not equal to -dM And I know your reason why you used dM'. Wait a minute, I think I see the light. Could you please check my story below? A rocket initially has mass M and velocity v relative to an inertial reference frame. During dt, it ejects...
9. ### A system with varying mass - a rocket

Hi Ho! ^_^ Mmm... about an hour ^^;; Ummm... I know that this is all about the sign but what make me wonder actually is not the sign but the author's reason. Why did he use M+dM when he knew that the rocket loses its mass? If I were the author I would use M-dM because I know that the...
10. ### A system with varying mass - a rocket

In Fundamental of Physics 6th ed. by Halliday, Resnick, Walker pg. 181-183, the section is about systems with varying mass: a rocket. It is written: Is it okay if I change M+dM with M-dM because I know that the rocket loses its mass and -dM with dM because the exhaust product has mass in...
11. ### A system with varying mass - two long barges

Hi Ho! ^_^ Hehehe... okay! I'll solve it! ^^v The fast barge doesn't change the speed of the coal. Thus, Ff = 0 N The slow barge must change the speed of the coal from 20 km/h to 10 km/h. Therefore, Fs = { [ vs * ( Ms + dm ) ] - [ vs * Ms + vc * dm ] } / dt Fs = (vs - vc) * (dm /...
12. ### A system with varying mass - two long barges

Aaah, now I see the picture! ^_^ I really got it! ^.^ The things below are the step how I grasped the idea. In the last question, in my mind the barges do change in speed during the shoveling process. Barge A accelerates and barge B decelerates. Yup! In the first thread, my focus was...
13. ### A system with varying mass - two long barges

Hi Ho! ^_^ Mmmm... I think I got it a little. About the another example, the answers are (a) There's no additional force required to maintain the speed of the barges. Because there's no change in momentum. (b) The coal doesn't change momentum. Am I right? To make me sure that...
14. ### A system with varying mass - two long barges

|-------\ | Mf > -> vf |-------/ |-------\ | Ms > -> vs |-------/ Two long barges are moving in the same direction in still water, one with a speed of 10 km/h and the other with speed of 20 km/h. While they are passing each other, coal is shoveled from...
15. ### Work-Energy Theorem question

Hi Ho! ^_^ Assuming that there's no frictional force on the incline, you got the right answer. You forgot to include the minus sign for the acceleration. Thus, -f = ma -(mu)mg = m(-3.50) The sign cancels and you'll get mu = 0.357 (I found it to be 0.356). If that's not the answer...
16. ### Work-Energy Question

Hi Ho! ^_^ I found a question like this in Fundamental Physics 6th Edition by Halliday/Resnick/Walker. Page 148-149, Sample Problem 8-4. Therefore, I can answer your question. 1. Let's take an isolated system consists of: earth-bridge-sandbag-cord. 2. Because it's an isolated system...