# Search results

1. ### How long does it take to stop the car

The first step in the problem is to draw your free-body diagram and label all of the forces acting on the car. Basically you have 3 forces, the force of the weight, the force of friction, and the normal force on each tire. Because each of these forces are the same on each wheel it is only...
2. ### Exit velocity of a water pipe.

Fred is correct in saying that the velocity is so high because you are neglected the effects of viscous flow, which in real life application is quite significant. However if we want to use this concept you have to know several things about the pipe such as its roughness coefficeint \epsilon...
3. ### Expressing moment as a vector in i,j,

You are getting confused I think between what a vector is and what a point is. A vector only describes the direction something something is acting in. Not at which point it is acting it. Your answer is still incorrect because of the direction in the k direction. Use your right hand rule...
4. ### Help physics homework

Yes thats correct but use -9.8 for gravity so k becomes a positive number that way -k is actually a negative value. Understand?
5. ### Differential Equations L^(-1) { (3s-4) / (s(s-4)) }

The thing about Laplace transforms is that you basically need to just know thier identities and properties. Thats the only way to do them really. Especially thier inverse. Go to your book and find the table that shows the Laplace Transform identities. The inverse Laplace just changes the...
6. ### Expressing moment as a vector in i,j,

If the moment is in the Z direction then the problem is already solved. Remember that in i,j,k coordinates x=i, y=j, z=k. Therefore if the moment is acting in the z direction what would your vector be? Use the right hand rule to figure out the direction of the moment. Hint (curl your...
7. ### Bernoulli's Principle of a pipe

Ok you know that P_1+\frac{1}{2} \rho_1 V_1^2+\rho_1 g h_1 = P_2+\frac{1}{2} \rho_2 V_2^2+\rho_2 g h_2 And Q_1 = Q_2 = V_1 A_1=V_2 A_2 Because of steady flow So you have the P1 and P2 you know the density and the height I assume would be the same. Therefore from Bernoulli's...
8. ### Dirac Delta Function

Sweetness. Thanks for the help. On a side note my test today was completely void of the delta function. Infact it only had 4 questions. One was a second-order linear non-homogenous ODE with a discontinuous unit step function that you needed to use a Laplace transform to answer so that was...
9. ### Many students pursue Mechanical and Electrical Engineering rather than

I would actually like to know whether or not that is the real reason. What are the upper level course's Mechs take? I've heard thousands of times that ME and EE have wider applicability but I don't know wheter or not thats true. For comparison, here are the courses I take as AE starting with...
10. ### Test rig to demonstrate propulsion

Mr. P, What I was saying is that if you were to model an engine or a pump or whatever you would have certain things that will remain constant based on the model and your real life situation. These parameters such as viscosity, density, and pressure. Therefore you can cancel them as long as...
11. ### Dirac Delta Function

Ok I think I might be getting this now. Here's one I was working on \int_{\infty}^\infty\exp(2t)\cos(t) \delta(t)f(t) \ dt I got the answer of 1. My reasoning... The way I understand is when evaluating the integral of a delta function of \delta(t-a) it equals f(a) in this case a=0 so...
12. ### Dirac Delta Function

Ok I suppose my specific question is how do you take the Laplace of the delta function. I'm just not getting it.
13. ### Test rig to demonstrate propulsion

I am just finishing a fluid mechanics course this semester where we talked about modelling things that you are talking about. The first thing you want to do is to determine what parameters are important to you and how they depend on eachother. Take thrust for example. You want to find the...
14. ### Dirac Delta Function

I have a test in Diff Eq. tommorow and part of the test is inovling the Dirac Delta function. I have no clue as to what it is at all. More specifically its Laplace and Inverse Laplace. If anyone could explain to me what the delta function is and how to use in in diff eq and what are its...
15. ### Air Pressure and flow to power calculations?

Patm is Atomspheric Pressure g is gravity of course h is height
16. ### CO2 propulsion

Well when I was in highschool we built CO2 and they were launched in a similar fashion as was originally described. If I remember correctly the car's minimum weight was 55 grams and I think some of them went as fast as 50 mph. I hope that helps.
17. ### Need Ideas

You might want to check out the Technology Studen Association (TSA) http://www.tsaweb.org/ I was involved in it my entire four years of highschool and it was awesome. They have regional, state, and national conferences. Alot of the activities listed above are TSA activities.
18. ### Dynamics smooth circular bar Problem

Yea, the mass is a ring attached to the circular bar. I suppose its like a washer or something attached to the bar. The bar is spinning and object is help there by the force of the radial acceleration and perhaps, the force of the tangential acceleration. Although I am not entirely sure there...
19. ### Dynamics smooth circular bar Problem

The circular bar is rotating causing a radial accelertation which in turn causes a force that counteracts the component of the object's weight in the normal direction. However, my intution is playing tricks on me because I don't think I can ignore the component of the objects weight in the...

21. ### Dynamics smooth circular bar Problem

Thanks for the help...but there is no string the mass is just held there by the Forces of the rotating bar. I'm not sure if that would change what you told me.
22. ### Dynamics smooth circular bar Problem

I think I did this problem correctly however I am not 100% sure. Unfortunatley the Dynamics book that I have only gives answers to even numbered problems and I cannot check me work. Anyway here is the problem from the book. The smooth circular bar rotates with constant angular velocity...
23. ### Questions on Mechanics (moments)

A moment is the cross product of force and distance or the magnitude of the moment is Fd*sin(b) where b is the angle between the force and the moment arm (lever). Think of it this way: If you want to push a door open you would push perpendicular to the door at the farthest point from the hinge...
24. ### Dynamics Help

Awesome thanks for the help. Everything worked out nicely.
25. ### Dynamics Help

For some reason I just don't get my dynamics homework. Here are the few problems I am having. Problem 1: A river is flowing north at 3 m/s (uniform current). If you want to travel in a straight line from point C to point D in a boat that moves at a constant speed of 10 m/s relative to the...
26. ### Torque exerted by cranksahft on load

Ok lets look at the units here. I'm going to use the FLT system (Force, Length, Time). A Joule is FL Your unit of power is FL/T And of course your unit of time is T So the units for you equation are ((FL - FL) * (1) * (FL/T)) / (T * (FL/T)) = FL/T The equation basically equals...