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• Users: Leong
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1. ### Why does a log float horizontally?

Original question from the book: Logs dropped upright into a pond do not remain upright, but float ‘flat’ in the water. Explain. A long log can float vertically but this position of equilibrium is unstable. So, a slight tilt will make it tilt further from the vertical position until it reaches...
2. ### I Sin x < x

:ok::thumbup:
3. ### I Sin x < x

Thank you very much for the explanation.
4. ### I Sin x < x

Given that 0 < sin x < x is true for 0 < x < π/2. From the above, can we conclude that 0 < sin (x/2) < x/2? How about 0 < sin (x/5) < x/5? Why? How about 0<sin 3x < 3x ? Why?
5. ### Photoelectric effect

Would you mind explaining how the electrons flow in the circuit & how the current flows in the circuit?
6. ### Photoelectric effect

When the emitter is connected to the positive polarity of a battery, it is said that 'Some high speed electrons are still able to reach the collector and therefore there is flow of current.' (1) What is the flow of electrons like in this case? I thought electrons are supposed to flow from...
7. ### Tension in a spring

I think if you draw a free body diagram for a coil in the middle and another one for the coil near the wall, you may find that the sum of the tensions (the pulling force that acts on the coil) for the coil near the wall is greater than the sum of tensions that pulls the coil in the middle...
8. ### Normal force by a spring

Thanks for the explanation which I cannot find anywhere. Thanks to everyone who replied to my post.
9. ### Normal force by a spring

Do you mean spring force or normal force or both as the force on the book exerted by the spring on the book?[/COLOR]
10. ### Normal force by a spring

If there is no platform, just the book on the spring, will there still be a normal force on the book other than spring force and the weight of the book?
11. ### Normal force by a spring

Perpendicular
12. ### Normal force by a spring

Homework Statement A vertical spring is fixed on a table. A book is put on the spring. The book compresses the spring until static equilibrium is reached. Question: Is there a normal force exerted by the spring on the book? Why or why not? Homework Equations The Attempt at a...
13. ### Electrical and gravitational forces of protons

When r approaches zero or when they are very close to one another, the gravitational force is as large as the electrical force. Both the forces approach infinity. or When r approaches infinity or when they are very far apart, the gravitational force and the electrical force approach zero. Make...
14. ### Problem regarding centre of mass and linear momentum.

You're good. You can see the different reference frames and introduce relative velocity.
15. ### Problem regarding centre of mass and linear momentum.

What you said is very true.
16. ### Problem regarding centre of mass and linear momentum.

square root of [2mgh/(M+m)]?
17. ### Hooke's law

Thanks for explaining, again.
18. ### Hooke's law

Let say I have a spring with spring constant of 10 N/m. I compress both ends with the same force so that each end compresses by 5 cm. Thus, the total compression is 10 cm. If I use F=kx where x is the total compression, then the spring force acting on each of my hand is 1 N. If I use F=kx...

20. ### Hooke's law

1. Are the spring forces at both ends of a spring always equal in magnitude? 2. If yes, then the external forces at both ends are also the same in magnitude, aren't they? (Based on Newton's third law) If no, how to find the two different spring forces at each of the end? 3. If the...
21. ### Work-energy theorem

I have done some reading to find the answer. This is what I got: 1. Work-energy theorem applies only to particles. 2. Objects subject to friction cannot be treated as particles. 3. Thus it is wrong to apply work-energy theorem to objects subject to friction.
22. ### Work-energy theorem

If we include heat in the equation, how will it fix the equation? Or if the table is free to move, then it will move and gain kinetic energy of 1 J?
23. ### Work-energy theorem

So, the table should move to fix the -1 = 0?
24. ### Work-energy theorem

A block (2 kg) is moving with an initial speed of 1 m/s on a horizontal rough table comes to a stop eventually. Applying work-energy theorem to the block-table system, we obtain Change in the kinetic energy of the block + Change in the kinetic energy of the table = Net work done on the...
25. ### Conservation of angular momentum

Homework Statement When a block is dropped to a disc that is rotating with a constant angular velocity about its centre, at the end, we know that both of them will rotate with the same new angular velocity which is slower than the previous one. Question: What is the force that makes the...

27. ### Work done by force acting on a spring

I know that s is the displacement of the body, not the force. Whether there are 2, 3 or 10 forces acting on the body, the body will only move in one direction and therefore one displacement. Thus, when we find the work done by each of the force, we use the same s, the displacement of the body.
28. ### Work done by force acting on a spring

Net work done on a body = (F1 dot s) + (F2 dot s) + (...) = (F1 + F2 + ...) dot s = (Net force) dot s = Work...
29. ### Work done by force acting on a spring

I know that the net work done on a body equals to the sum of the work done by each of the forces acting on the body which also equals to the work done by the net force acting on the body. I can't see the whole picture. I don't get the same thing when I view it from different angles. Something...
30. ### Work done by force acting on a spring

Then force D will do some work on the spring since the point of application is moving because this end of the spring is oscillating together with the mass. So, there will be a net work done on the spring. Force E does zero work on the spring while force D does some work on the spring. So, there...
31. ### Work done by force acting on a spring

No. I just wondered when I read a book and did some exercises.
32. ### Work done by force acting on a spring

The net work done on the wall for sure is zero. Is there any relationship between the work done on the wall with the work done on the spring by the wall? I do not know anything about that.
33. ### Work done by force acting on a spring

The wall is not moving. Its displacement is zero. Force E is exerted on the spring by the wall.
34. ### Work done by force acting on a spring

When the spring is compressed, that force is a push. When spring is stretched, that force is a pull.
35. ### Work done by force acting on a spring

Let say we have a horizontal mass-spring system oscillates without friction on a smooth surface. One side of the spring is attached / fixed to a wall. The other is where the mass is attached to. Let say we choose our system to be the mass and the spring (negligible mass), so our free body...
36. ### How to solve this trig equation

sorry. you're right all this while.
37. ### How to solve this trig equation

yes. you're right. cot (3pi/2) is not undefined. it is 1/undefined.
38. ### How to solve this trig equation

i don't think it is right to say that 1/undefined = 0.
39. ### How to solve this trig equation

When i substitute pi/2 into the original equation, cot 3x will be undefined. Can we take pi/2 as a solution?

41. ### Triangle question (2)

Coordinate geometry
42. ### Triangle question

1. A(0,0); B(a,0); C(0,a), M(0,a/2). 2. Slope of MB = -1/2 3. Slope of AP = 2 4. Equation of AP: y = 2x 5. Equation of CB : y = -x + a 6.Intersection of AP & CB is P(a/3, 2a/3). 7. BP: PC = 2:1.
43. ### Linear speed of a car Vr

If the tire makes 1 revolution, the car has traveled for a distance corresponds to 1 revolution. If the tire makes 2 revolution, the car has traveled for a distance corresponds to 2 revolutions. If the tire 17.4 revolutions in 1 second, what is the distance traveled? How much time is needed...
44. ### Simple velocity/motion question

Perhaps you should consider the air resistance (the drag force) and the friction to come out with a reasonable explanation that is consistent with your data.
45. ### Average Velocity of a meteor

no it is wrong too.
46. ### Average Velocity of a meteor

i think u will just have to wait.
47. ### Average Velocity of a meteor

you can't. only the moderators can.
48. ### Average Velocity of a meteor

figure attached.
49. ### Average Velocity of a meteor

find the inverse tangent is right. the two values are wrong and irrelevant.
50. ### Average Velocity of a meteor

I would try sketching a figure and locate the two given points on the figure. Draw the right triangle that is appropriate for figuring out the angle.