# Search results

1. ### Having trouble with this impedance problem

I'm not sure, but if you say that the tension of the dashpot is Z_d*(x_1 - x_2) , then this is the magnitude of the force the dashpot exerts on the strings. Using Newtons third law, the strings will exert an opposite and equal force on the dashpot. Thus, we would have Z_d*(x_1 - x_2) =...
2. ### Resistance + Mechanics problems

I am currently trying out for the US Physics team, and am working on some practice exams. I was wondering if anyone could offer some assistance on the following problems below: Problem A2 http://www.compadre.org/psrc/evals/IPO_Exam_2_2003.pdf Problem's A4 and B1...
3. ### Suspension cable exerts no net horizontal force on the towers?

The wording in your description may be slightly confusing to posters. Perhaps if you could include a diagram of the problem. Anyways...when you work with statics...always remember that about any point, the torques always = 0. Also, sum of the x forces = 0 and sum of the y forces = 0.
4. ### Work and Friction

Net work done on object = (horizontal component of 118 - frictional force) * distance Net work done on object = change in kinetic energy (work-energy theorem)
5. ### Save Tarzan and Make sure his Vine doesnt break(HELP NEEDED)!

The rope must also overcome the force of gravity acting on Tarzan when he is at the bottom of the arc. Thusly, the tension of the rope = Fcent + Fgrav at this point.
6. ### Can anyone help?

The question is asking for "when", which implies time. THus, take the derivatives, and solve for t when the derivative = 0. AFter you have found your values for t, then you will need to test whether the value is a maximum or a minimum. (if you don't find a max or min. with these values...
7. ### Initial speed physics help

...x = v cos (theta) t divide both sides by vcos(theta)...and you get t = x/(v cos (theta) Now plug this into the equation for y... When you do this, you should be able to solve for initial velocity.
8. ### What fraction of its kinetic energy is rotational?

To start off... Gravitational Potential Energy = Linear Kinetic Energy + Rotational Kinetic Energy ...Rotational Kinetic Energy = 1/2 I w^2 w(its called omega) = v/r I of Sphere = (2/5)mr^2... ..thusly...Rotational Kinetic Energy = (1/2)[(2/5)mr^2][v/r]^2...which simplifies to...
9. ### I need some serious help

Tarzan is moving in an arc...that means that centripetal acceleration is involved...(since he's moving in a circular direction). Thusly, there is a centripetal force acting on Tarzan (Fc = mv^2/R) and the graviational force as well (F = mg)...basically...work with that info...and also...try...
10. ### Impulse thrust calculations from pressure bottle

P = F/A; Change in momentum = Impulse = Force * time Change in energy = Work = (Force)(distance)(cos (theta))...since this a rocket..the force will most likely be in the same direction as the movement...so...cos(0) = 1...and you have... Work = Force(distance). Or, since you know the...
11. ### Work and energy problem

...think...when the car is at rest...what forces are acting on it? What forces are acting on the ball? Is the ball in equilibrium? ...when the car is accelerated up the incline...how does this acceleration affect the ball (remember, princaple of equivalence?)
12. ### Mass on Spring

The force a spring exerts on an object is F = -kx.
13. ### Power and maximum power problem

yeah...sorry 'bout that..I left out the sumation part... but basically follow Spectre5's advice...free body diagrams are essential to solving most force related Physics problems
14. ### Power and maximum power problem

F = ma Thus, when the car is accelerating, the force acting on the car not only must overcome the force of gravity, but it also must accelerate the car.
15. ### Potter wheel

Looks like you're using mr^2 for the moment of Inertia...which would work if it were a ring.. ..however, the moment of Inertia of a thick solid disk is: I = 0.5mr^2.. ...hope that helps!
16. ### Exploding object (momentum problem)

The time of explosion is when the vertical velocity = 0 (since it is at the top of the path). Use this info when calculating... part B just involves finding the kinetic energy of the object before it explodes, which is: KE= 1/2mv^2 THe KE afterwards would just be the same thing, except...
17. ### Law of conservation of momentum

looks good to me. :-D
18. ### Angular velocity of a ferris wheel

How did you get a mass of 11.71 kg? The passenger's normal weight is 367 Newtons...and weight = mass * g.
19. ### Min. speed

Now, remember...this is minumum speed... ...so the tension of the string is mimumum, or zero when the ball is at the top of its path (thus, only the force of gravity would equal the centripetal force.) With this knowledge, draw a free body diagram of the ball when it is on the top of the...
20. ### Velocity of an electron

Well...the method I just gave you is based on classical mechanics, which basically works ok for anything << speed of light. However, anything remotely close to the speed of light (such as something with a speed of 0.1c)...would require the relativistic definitions... In classical mechanics...
21. ### Need help with college interviews

Yeah...what Moonbear said...and basically stay relaxed...have good eye contact, be friendly and I'm sure you'll do fine. :-D
22. ### Airplane flying in a circle

Looks good. :-D
23. ### Free-body diagram to identify the forces acting on the car

k...in this case...the force of gravity = centripital force...which I think you have figured out already... You are correct in stating that Centripital force= mv^2 / R Now draw a free body diagram to find the force of gravity...its not mg tan (angle)...its mg * something... ...work from...
24. ### Velocity of an electron

Yes. You can find the velocity of an electron accelerated through a particular potential difference. Remember that: potential differerence (aka voltage) * charge = Change in potential energy (U)... Since you know the charge of an electron...you can simply multiply this by the...
25. ### Airplane flying in a circle

Remember that A(centripital) = v^2 / R... ...so your answer to problem 1 looks correct. On problem 2, how did you go from a velocity of 48.1 m/s to that of 4.8 m/s? The mass would just be the pilots mass...because its asking for the centripital force acting on the pilot.
26. ### Help: Kinetic Energy

Try to draw a free body diagram. In one direction, you have 722.1 Newtons acting on the piano. In the opposing direction, you have the force of gravity. F = ma Mover's force - force of gravity (sin 9.1 * mg) = Net Force Acceleration = Net Force/Mass ...with this acceleration, just...
27. ### Work Done by the Gravitational Force

Work = Force * distance Remember, you only need to multiply stuff by the cos (angle) or sin (angle) to get that component of force so it matches up with movement. In this case, the 60 N applied in the opposite direction as the movement...so you don't need to find any of its components...
28. ### Crossing a River

First, you mentioned the distance between B and C as 150 m, and later said it was 1500. A second thing to keep in watch, when you converted m to km, and multiplied it by cos(45) or sin(45), you changed distance to velocity by adding the "/h". Really, 1.5km * cos(45) = 1.06 km Keep in mind...
29. ### Yet another free fall question.

Uhhhmm...there is no need for the quadratic equation on this problem. It can be solved by using the general kinematic equation in most Physics textbooks. Since the stone is at rest and has no initial velocity...we can use: distance = (1/2)at^2 We know the distance the stone travels...
30. ### Quick Starter Questions

Vf^2 = Vi^2 + 2a(d) d = Vi (t) + .5at^2 These are two of the general equations for kinematics.
31. ### News Fahrenheit 9/11 could be disqualified from Oscars

I think Moore only cares how well the film does before the upcomming November election. Since the oscars will be afterwards, I think whether his film is nominated or not will probably not bother him.
32. ### Baby Universes in labs

I think the 10 dimensional universe theory (4 macroscopic dimensions, and 6 microscopic dimensions) has to do with string theory, which has not yet been proven experimentally (Which would be rather difficult). I suppose the latter explanation is how general relativity would explain it. I...
33. ### Moles in a Cat

There are 6.022 * 10^23 atoms in 1 mole. Molar mass of hydrogen is around 1 g/mole...carbon is around 12 g/mole...and oxygen is about 16 g/mole... You have 12,000 grams...you can find the moles and then thus find the atoms. :-D
34. ### Displacement and Velocity

Blackmamba, write an equation describing the distance between the bear and tourist, and make it relative to time: distance between bear and car = 20 m -(bear speed * time - runner speed * time)...work from there to find the time. With time, and runner speed, you can find distance...
35. ### A question about average velocity?

Actually balooza is correct in reasoning why (V(i) + V(f)/2) works only for velocity that can be represented by a linear line.
36. ### Instantaneous velocity animation

No...s^2 is simply a unit. It is NOT a variable. You are taking the derivative of the function with respect to the variable t, so try to envision that particular term as 2.20t^2...and the derivative of that would be 4.40t.
37. ### Hard physics problem

yeah...i know. ;-D Most people probably would solve this problem like you did...but I thought it would be interesting to post a method that doesn't involve a big 5 equation derived from calculus...and uses, in a sense, basic mathematics to find acceleration.
38. ### Hard physics problem

Needpersonhelp's method works, largely cause in this case the acceleration is constant. Another method that will work is outlined below: 14.4 m 25.6 m 2 s later 40 m Another 2 s later 57.6 m Another 2 s later Now, find the differences in the distances...and you...
39. ### Simple Velocity Problem

Integrating a function is a method of finding the area beneath it. There's an elegant proof found in most calculus books that connects Rieman's sums (which is really just adding a bunch of infinately small shapes together to find area) to integration. Thus, since integration is much simpler...
40. ### Simple kinematics sprinter problem

actually, based on your answer of a = 4.8 ft/sec^2...it appears that you must have used the above method, or a similar one...but instead of having the length be equal to 300 ft (100 yards)...looks like you had it equal to 100 ft. So anyways, I'm willing to guess that you had your method...
41. ### Simple kinematics sprinter problem

david90, here's a way you can solve it algebraicly: For the first 2.5 seconds, the sprinter is accelerating...thus...we can describe that part as distance = (1/2)at^2, with t = 2.5 it would be = (1/2)a(2.5)^2 For the last 7.1 seconds, we know that the speed is both constant and...
42. ### Simple kinematics sprinter problem

sorry david, but 12 ft/sec as a max speed is a little to slow...this guy here's running 300 ft (100 yrds) in 9.6 seconds.
43. ### Falling objects puzzle

The stones are thrown at the same horizontal speed, but the vertical heights of the buildings are different. The time it takes for the stone to hit the floor has nothing to do with horizontal speed (now we are neglecting air resistance here), but only to do with the height with which it was...
44. ### Nice NSL problem w/ calculus

Galileo is correct with his answer (isn't he always correct...i mean...about moons and Jupiter...acceleration on Earth independent of mass...except maybe for his non-relativistic work on motion for frame of references). Anyways, the answer to the problem is that the angle = arctan u. If the...
45. ### A question about Change in Momentum

yeah...knowledge of power...you calculations look fine to me...as force is a vector, so a negative value should simply mean that it is opposite to the motion of the car.
46. ### Free fall question

You could also solve this way: let t = time it takes to fall. since x = .5gt^2 (one of the general motion equations) h = .5g(t^2) .75h = .5g(t - 1)^2 (since time will be t-1 when it has fallen .75h) just subtract one equation from another to get .25h = .5(t^2) - .5(t - 1)^2...and...
47. ### Formula equations and momentum!

Princexcharles...1000 ms is equal to 1 second...so 30 ms would be 0.03 seconds. Also, Physicsneededhelp...for future reference, make sure you check your units before you go through with your calculations. In your earlier post, you were dividing meters/seconds by miliseconds...make sure all...
48. ### Mechanics Physics

Yeah...everyone above has given some pretty good advice...I just want to emphasize that it is VERY important to do practice problems...the more problems to do...the better situation you'll be in.
49. ### Force questions?

terpsgirl...for the first problem...use the equation that states that impulse = change in momentum...the equation is: Force * time = change in velocity * mass. Think of what the original velocity is, and the final velocity...and u should be able to find the change in the velocity...
50. ### Simple harmonic motion in a rocket?

np man...anytime :-)