# Search results

1. ### Our class has only completed ~50% of the Physics B Curriculum

I didn't take AP Physics so I wouldn't know but I am taking an introductory physics class right now. I am not sure how hard AP Physics is but that sounds like a lot of materials. I would say optics is probably the easiest topic at least as far as math in concern. The formulas (at least in my...
2. ### Work done in an Isobaric expansion

I am sorry I can't really follow the work. Please include the units. I would approach this problem this way... First of all, I would sketch a P-V diagram. It starts at some pressure and volume and then undergoes an isobaric expansion tripling its side. With p on your vertical axis and v on...
3. ### Glasses to fix near points and far points

If -2.62 is 1/f and the answer is indeed .34 for as in the answer key then o must be greater than 3 meters away. How is that possible? Do I somehow combine that 1.98 m with the other part a, which is .82 meters?
4. ### Finding length and longitudinal magnification

Homework Statement A small object of length dL is placed on the axis of a converging mirror of focal length f. The center of the object is a distance o from the mirror. Determine the length of the image and thus effective determine a longitudinal m' = dL'/dL for the lens. Homework...
5. ### Glasses to fix near points and far points

Thanks for your help. I just realized that I need help for part b as well. b) 1/f = 1/o + 1/i The person's far point is .6 or .58 from the glasses. I want him to see at .25 m or .23 m from the glasses. 1/-f = 1/.58 + 1/-.23 1/-f = -2.62 1/f = 2.62 that is the power. I am...
6. ### Glasses to fix near points and far points

Homework Statement a)A person has a near point of .6m and far point of 2m . What power of glasses would be needed for the person to see infinitely far away. Assume that glasses are 2cm from the person's eyes. If the person used those glasses, what would his new near point be? b) What...
7. ### Mixing ice, steam, and water and find equilibrium

Thank you very much for the help
8. ### Mixing ice, steam, and water and find equilibrium

Homework Statement .15 kg of steam at 100 degree Celcius is mixed with .2kg of water at 50 degree and .2 kg of ice at 0 degree. Determine the final temperature and phase(s) of the final state. Assume that no energy is lost to the surroundings. Homework Equations The Attempt at a...
9. ### Roof withstanding a storm

Homework Statement Someone is putting a small shed in their backyard. The roof is not nailed down so gravity alone is holding it down. The wind suddenly flows across the top of the roogf at 20 m/s. The air inside the shed is 1.01 x 10^15 Pa, the normal atmospheric pressure. The roof has an...
10. ### Density and simple harmonic motion

Never mind I got it now. Thanks a lot for your help.
11. ### Density and simple harmonic motion

For the object at rest I got B - mg = 0 When it's pushed down B - mg -f = -ma Since B =mg f = ma I already know this though so how does it help prove that it's in simple harmonic motion with a repeating pattern?
12. ### Density and simple harmonic motion

When the object is at rest, I have mg pulling down and buoyant force pushing up. They are equal in magnitude. The net torque is also zero. When the object is pushed down I have f pushing down, mg pulling down, and buoyant force pushing up. This extra f is enough to push it down. My net...
13. ### Density and simple harmonic motion

Homework Statement A mass of density d floats in a liquid of density d_L. The mass is then pushed down a distance x and let go. Use Newton's Second Law to demonstrate that the mass will undergo simple harmonic motion. Recall that the SHM equation is d^2x/dt^2 + w^2*x = 0. Assume there is...
14. ### Releasing a sphere from water

Thanks. I will try it again.
15. ### Releasing a sphere from water

Homework Statement A 1kg hollow sphere of volume .00419m^3 is released from rest at the bottom of a 2m deep pool of water (density of water is 1000kg/m^3). The sphere accelerates upwards and flies out of the pool. How high does it get above the pool before coming down. Ignore the brief time...
16. ### Fluid displacement

Homework Statement A small child floats in a boat in a swimming pool. The boat contains an anchor The child drops the metal anchor into the water and watches it sink to the bottom. Meanwhile, the water level in the pool (measured by its height on the side of the pool) actually drops. Why...
17. ### Drawing free body diagrams for pendulum

It means that at most the pendulum travels 30 degrees in either direction from equilibrium point.
18. ### Drawing free body diagrams for pendulum

Homework Statement I have to do this for a lab. Draw and label the free body diaggram of a pendulum when it is at its maximum amplitude of 30 degrees. The magnitudes of the vectors must be correctly scaled and the directions correct. Homework Equations The Attempt at a Solution...
19. ### More static problems

I have no idea on how to start these two problems. I haven't done any work, but please give me some hints on how to get started. The two problems are here http://viewmorepics.myspace.com/index.cfm?fuseaction=viewImage&friendID=128765607&imageID=1461065539 For problem 14, the anskwer are...
20. ### Find angular velocity

Thanks. For part b, I still don't know where v^2/gl come from. G is an acceleration due to gravity, l is a length, and v^2 is m^2/s^2. After division, v^2/gl is just a number with no unit. However, I don't know where the term come from.
21. ### Find angular velocity

I made some mistakes. L = 2r, r = (1/2)L w=v/r w^2=v^2/r^2 or v^2/(1/2*L)^2 = 4v^2/L Is M in this case 2M1 since we have two masses in the system before collision. Should the mass be 2M1 + M2 after collision?
22. ### Find angular velocity

Angular momentum = m*r*v I know that I for a rod is (1/12)ML^2 so L = Iw then L = (1/12)ML^2*v^2/L^2 L = (1/12)MV^2*L^2 r = 2L If I have IW = I_f*W_f W_f = I/I_f * W W_f = (1/12)ML^2/(I_f) * W I am stuck. I don't know what to do from here.
23. ### Find forces in ladder

I am having problems with this part. I know that N_a + N_b = Mg, and I know that N_a is greater than N_b because the person is closer to A. N_a + N_b = 852.6 Since tension is internal as you said, I should not include it in the torque equation - right? So 0 = -T_na + T_nb -...
24. ### Find forces in ladder

I know that net torque is zero 0 = -T_na + T_nb -T_mg + T_t I got 0 = -1.25N_a + 1.25N_b - .3123*mg + T_t I know that T_t is there, but I don't know the direction. Is it pushing right or left? After I get this, do I plug into those equations to get the rest. The answers are...
25. ### Find angular velocity

The problem is problem 6 at http://viewmorepics.myspace.com/index.cfm?fuseaction=viewImage&friendID=128765607&imageID=1460003525 A long thin rod of mass M and length L with two balls of mass M1 (same mass for both) attached is allowed to rotate about the horizontal axis shown. The bar is...
26. ### Find minimum force to raise wheel

With net torque, I have mg*R + F(R-H). So F = mg*R/(R-H) From the way it seems, I got the F(R-H) part right, but mg*R is still not quite right. HOw do I get SQRT(2RH-H^2)?
27. ### Find forces in ladder

Yes, http://viewmorepics.myspace.com/index.cfm?fuseaction=viewImage&friendID=128765607&imageID=1460657842 I am sorry for leaving it out.
28. ### Find minimum force to raise wheel

I am not sure about this...is the moment of inertia with respect to the contact point MR^2 + R^2 with the parallel axis theorem? I know that whatever force the wheel pushes against the contact point, the same force will push the wheel back. But I am not sure about how to find that force for...
29. ### Find forces in ladder

Each side of a stepladder is 8m long and there is a hinge at the top. An 87kg man is 6m up one side and there is a 2.5m long rope connecting the two sides. The rope is exactly halfway up the ladder. Assume that the floor is frictionless and neglect the weight of the ladder. Find the tension...
30. ### Find minimum force to raise wheel

What minimum force F applied horizontally at the axle of the wheel is necessary to raise the wheel of mass M and radius R over a step of height H. A picture for this is at http://viewmorepics.myspace.com/index.cfm?fuseaction=viewImage&friendID=128765607&imageID=1460005538 The answer...
31. ### Find the tension with using forces and torques

Okay, thanks very much for your help tonight.
32. ### Find minimum force to tip block

Oh I see now. Thanks very much.
33. ### Find the tension with using forces and torques

I am not sure if this is right. Mg should be from the center of the pole. So the distance is 7.5/2*cos(37). If I plug this back in, I would get T2 = 48.38 N. Is this correct? I know that T2 = m2*g so I should be able to find m2. However, how do I find tension of the first rope since...
34. ### Find minimum force to tip block

I would have mg pointing down from the center of the block and N pointing up. I would also have friction pointing to the left. The distance between the center and the rotational axis is H. However, why do we multiply this mg by L when L is the horizontal distance. Does this have anything to...
35. ### Find the tension with using forces and torques

When I do that I get 8*9.8*6.31 + 5*9.8*7.5* cos(37) = 7.5cos(37) * T2 T2= 88.19 This answer is incorrect. The answer key says that the answers in this problems are 139N, 49N, 139N, 127.4 N for each of the forces. 88.19 is not any of these. What did I do wrong?
36. ### Find minimum force to tip block

A force F applied at point A is just large enough to tip over a block of mass M. The block will rotate about its bottom right corner. Find the magnitude of F. The picture for this is problem 13 at this link...
37. ### Find the tension with using forces and torques

A traffic light hangs from a structure shown at http://viewmorepics.myspace.com/index.cfm?fuseaction=viewImage&friendID=128765607&imageID=1460004546 The uniform aluminum pole has a mass of 8 kg and is 7.5m long. The traffice light has a mass of 5kg. The cables are massless. Cable 1 is...
38. ### Static equilibrium and a ladder

A ladder leans against a frictionlee wall. If the bottom of the ladder is pushed closer to the wall (so theta increases) which of the following change? Why or why not? Assume the ladder is in static equilibrium. a) Normal force exerted by the ground b) Normal force exerted by the wall...

Thank you.
40. ### Find angular velocity using angular momentum

A 20kg girl stands on a large turntable 4m from its center. The turntable has a moment of inertia (about its roation axis) of 200kgm^2. Assume that the girl is a point mass. a) Assume that the girl and turntable are rotating at 1 rad/s. If the girl walks inwards to a radius of 3m and...
41. ### Angular momentum

A 2kg object has a position vector r = -4t i + 3t^2 j (m). Find its angular momentum relative to the origin as a function of time. The correct answer is -24t^2 k (kgm^2/s). I know that L = r*p and p is mv so I differentiate r to get v v = -4 i + 6t j do I just multiply 2 and the...
42. ### Find axis to minimize moment of inertia

For part 2, I know that I = I_cm + mh^2, where h is the distance between the axes. So is h, L-r in this case? How can I get I about an axis through M2. Is it I = M2*L^2 + M1*(L-r)^2 ?
43. ### Find axis to minimize moment of inertia

Wouldn't I use the formula I = Mx^2 then where x is the distance down from the rod?
44. ### Find axis to minimize moment of inertia

Two masses (M1 and M2) are connected by a thin massless rod of length L. a) Determine the location of an axis perpendicular to the rod) which minimizes the moment of inertia of the system. The answer is "with M1 at the origin x = M2*L/(M1+M2) I know that I = Sum of ( M1*r1^2)...
45. ### Another yoyo question

Yes. So I have to include both in the problem. The given R is the outer radius, and the inner radius is not explicitly mentioned.
46. ### Another yoyo question

I know that the yoyo is a cylinder that spins counter clockwise going down and clockwise going up. It is attached to a fixed place a tthe top. I don't know what I am missing.
47. ### Another yoyo question

A yoyo is allowed to drop freely with a string held fixed in place at the top. Assume that the yoyo is a uniform disk of mass M and radius R. 1) Use Newton's Second Law to find the linear acceleration of the yoyo and the tension in the rope. My answer key says that the answers are 2/3 g...
48. ### Motion involving both translation and rotation

I don't really understand what do. From what you told me, The net force in the horizontal direction is ma, with friction being mu*mg The net torque is I*(alpha), and I know that I for a sphere is (2/5)MR^2 alpha is a/R so I = (2/5)*MA*R and F = mu*Mg The answer has a 12 and...
49. ### Motion involving both translation and rotation

Hello everyone. Thanks for all the help today. I know I have asked a lot of questions. This is my last one today. A spherical billard ball is sliding with a speed v_o. It has a radius R, mass M, and there is a friction coefficient mu. Determine the distance the ball travels before it...
50. ### Finding velocity taking the pulley into consideration

Since T1 is trying to cause the pulley to rotate counterclockwise, while T2 is causing it to rotate clockwise, would it work if I have T1*R-T2*R = I (-alpha)