[Yusf]

Please help me for national physics Olympiad bd.
I stood 7th in divisional round. With help, I hope iq will be able to place in the national round as well. This post is very very important for me.

1. A rocket accelerates at 10m/s^2. It releases a projectile. What acceleration (if any) will be of the projectile immediately after releasing?

I think it should be deaccelerating at about 10m/s^2. Am I right?

[ebaines]

How did you get 10 m/s^2? Are you thinking that the projectile continues to accelerate like the rocket? Or are you thinking about the projectile accelerating under gravity downward towards the ground in free fall?

[Yusf]

Yes. I think the projectile will accelerate downwards at 10m/s^2 under the influence of gravity.

[ebaines]

Right - once ejected from the rocket the only force acting on the projectile is gravity.

[Yusf]

2. Assume a trapezium type box filled with water. Let AB and CD be erect sides and parallel sides. Base is BC. Side opposite to Base is stanting and not parallel to BC. AB is .8m and CD is .6m. The base BC has mid point M. Determine the pressure on M.To find pressure by h×rho×g, what is the height I should take?Because the opposite side to BC is slanting. As pressure acts equally in all direction in liquid, I think I should ttake height of AB.

[ebaines]

Yusf - you're the Olympian - tell us what you think the answer is, and why. You may want to first think about a less complicated situation and apply the same principles: suppose the question asked about pressure in a pipe that is fed from a water tank h meters high - does it matter whether the pipe twists and turns?

[Yusf]

No, it does not matter if the pipe is twisted. We normally take height whether the pipe is twisted.

[ebaines]

No, it does not matter if the pipe is twisted. We normally take height whether the pipe is twisted.

Right. So your answer is...? Suppose I was to embed a pipe in the tank that ran from the upper-most point of the slanted lid of the tank to the point M - what would the water pressure at M be? By the way, all this assume the tank is a closed system, completely filled to the very top.

Another avenue of thinking: if the pressure at each point along the bottom varies depending on the height to the slanted lid, there would be a pressure gradient along the bottom. Such a gradient would cause water to flow, as fluids always flow from points of high pressure to low. Do you think there's flow going on from point B towards C? If there was such a flow, where would the water go once it reaches point C? If there is no flow, then that means there's no pressure gradient, right?

[Yusf]

Aaaha! This means the pressure is equal at all points and the pressure is to be calculated by the biggest height. This pressure is equal at all points of the base! Did I get it right?

[Yusf]

One minute, as in a reservoir, we know that pressure on the walls of the reservoir increases as we go downward. This is why the walls are made thicker at the bottom. As the pressure is different higher at the bottom, there is pressure gradient and water should try to go from place of higher pressure to lower pressure, right? But this does not happen. Is it balanced by gravitational pull? (Is the tendency of water to move with pressure gradient balanced by the gravitational pull?)Much obliged for answer.

[ebaines]

Aaaha! This means the pressure is equal at all points and the pressure is to be calculated by the biggest height. This pressure is equal at all points of the base! Did I get it right?

yes, that's right.

[ebaines]

One minute, as in a reservoir, we know that pressure on the walls of the reservoir increases as we go downward. This is why the walls are made thicker at the bottom. As the pressure is different higher at the bottom, there is pressure gradient and water should try to go from place of higher pressure to lower pressure, right? But this does not happen. Is it balanced by gravitational pull? (Is the tendency of water to move with pressure gradient balanced by the gravitational pull?)Much obliged for answer.

Water in a tank does not spontaneously flow from high to low pressure because this would mean the water moves up against gravity, which requires energy. Since water is incompressible you could start up a circulating current, with water rising along one edge of the tank and sinking against the other, but you can't have a situation where all the water spontaneously rises.

[Yusf]

Great. Everything now seems clearer than crystals! Thanks.There is something I have no idea about. Please explain them to me.Interference of waves.Magnetic axis.Calculate amount of electricity produced by generator. New Cartesian convention.Sign convention. Doping.

[ebaines]

I'm sure these subjects are covered in your text book. If you have a specific question please follow up.

[Yusf]

I'm sure these subjects are covered in your text book. If you have a specific question please follow up.

No. That's my problem. These are not in my book. Just to make things hard, they have put many topics which is out of my o'level syllabus. I have solved a lot of them by simple Google search. For these item as well, I made Google searches and there is a wiki of them too, but these are written in too complicated way (for me). Thus I could not benefit myself even a bit. Please explain them which has maths relating to them. You can skip those which has only theoretical topics. Because in the olympiad, I will only be asked to solved maths, no theory. And please do not explain in too high standard. You know my standard-an o'level student.

[Yusf]

Perhaps magnetic axis is the magnetic field lines?(I know about magnetic field lines.)

[ebaines]

Perhaps magnetic axis is the magnetic field lines?(I know about magnetic field lines.)

The magnetic axis is the line joining the north and south poles of a dipole magnet. It's also a line that if a second magnetic field is aligned with it causes 0 torque. Hope this helps.

[Yusf]

'0 torque' means no repulsion or attraction? Or something else? Please give me a formula to find out:Amount of electricity produced by generator. Inertia of an object. What is pole of a mirror? Will be really happy for your answer.

[ebaines]

Torque = force times lever arm length.

Generators are a huge topic - but in general a changing magnetoc field induces voltage on a wire. Altermnatively a wire cutting through magnetic field lines will have a voltage induced on it. So a generator tyouically has magnets and a set of wire windings that rotate about the magnet, causing a voltage to be induced.

Inertia of an object = its mass times its velocity

I don't know what "pole of a mirror" means.

[Yusf]

Does that mean that Inertia of object=momentum of it?
What about the inertia of a stationary object. (inertia is also the reluctance of a stationary object to start moving)

Today is the last day of my revision time. I have only some hours before I go to sleep. Please answer quick.