Physics Game - Page 2

[Mike555]

I am in physics, and I do not even know what that means. What exactly does that problem involve wasn't it supposed to be easy questions

[joshSCH]

um.. It's really not that hard. Involves some knowledge of angular momentum.. and calculus

[Infarction]

But, It might be better to make a new thread titled "Chemistry Game" anyways...

There's enough game threads as is. You can share. :twisted:

[GreenDay2001]

Actually, no one has answered my question yet:

"The position vector of a particle of mass 3kg is given by r(vector)= 4i+3t^2j, where r is in meters and t is in seconds. Determine the angular momentum and torque acting on the particle about the origin."

But, It might be better to make a new thread titled "Chemistry Game" anyways...

Not studied Rotational Mchanics yet, but have a bit of knowledge.
Is the torque equal 72Nm and angular momemtum equals 72t Js.

[joshSCH]

Not studied Rotational Mchanics yet, but have a bit of knowledge.
Is the torque equal 72Nm and angular momemtum equals 72t Js.

wow, good job. They are vectors, though.. the torque is 72Nm in the k direction, and the angular momentum is 72t Js in the k direction.
nice, your turn to post a question.

[GreenDay2001]

Oh, damn once again......I just forget to write direction, my habit is bad. Anyway, we get that using thumb rule.

My Question from Mechanics::
What minimum force has to be applied on the 3kg block horizontally to cause relative motion in all three blocks.

.......|----------------|
.......| ---------------|
.......| -----2kg -----|
.... -----------------------
....|--------------------- |
....| --------3kg-------- |
-----------------------------
| ---------------------------|
| --------7kg-------------- |
------------------------------------------

Coeff. of friction between 2kg and 3kg block is 0.2
Coeff. of friction between 3kg ang 7kg block is 0.3.
Coedd. of friction between 7kg block and surface is 0.

Although, the question is pretty simple, but its rather conceptual and I often get funny answers from my classmates.

[Duki]

meh, i probably did something wrong... i got 14.7N

if someone gets the right answer, will you post the equation you used? Haven't really done this yet... just basic single object friction movement.

[Rashakil Fol]

All conservation laws are basically the same.

If you don't have knowledge, don't pretend you do by making stuff up.

[joshSCH]

The conservation of energy/mass is the exact same law!! All the other laws are similar in that they involve that some quantity cannot be created or destroyed..

[joshSCH]

meh, i probably did something wrong... i got 14.7N

if someone gets the right answer, will you post the equation you used? Haven't really done this yet... just basic single object friction movement.

I also got 14.72N..

[Duki]

I also got 14.72N..

word? well... even if we're wrong, at least I won't feel as bad now. :mrgreen:

[GreenDay2001]

I also got 14.72N..

meh, i probably did something wrong... i got 14.7N

if someone gets the right answer, will you post the equation you used? Haven't really done this yet... just basic single object friction movement.

Well, guys you have got wrong answers.

[Rashakil Fol]

Relative motion? Relative to what? If relative to the surface, then there is no minimum (0 is the lower bound).

[GreenDay2001]

By relative motion in blocks i mean there is different acceleration in all three blocks, so relative to each other.

We ain't and can't consider all three blocks as one, as we do in several problems where force is applied at the lowermost block.

[Rashakil Fol]

If relative to each other, then 2.4 kg * g, or about 23.5 newtons on Earth.

[GreenDay2001]

Pretty near to the answer

[Rashakil Fol]

Near? Then my answer's wrong.

[Rashakil Fol]

Wait, you want all the blocks to be moving differently so that _no_ two can be the same?

[Rashakil Fol]

If so, then how about 12/7*1.5 kg * g, i.e. 25.2 N.

[GreenDay2001]

Well, you are right, all blocks must have different acceleration. But yes, I want minimum force. So when that force is applied then the acceleration of blocks will be somehow similer, I mean tend to be equal.

So just draw FBD's of all three blocks, get the acceleration, put your concept of static and kinetic friction.

[GreenDay2001]

If so, then how about 12/7*1.5 kg * g, i.e. 25.2 N.

You are almost right, just lagging behing by few points. I think you did right way. Shall I put the answer?? How did you do??

[Rashakil Fol]

Oh, I see the problem. How about 10/7 * 1.5 kg * g + 0.4 kg * g, i.e. 24.9 N.

[GreenDay2001]

Wrong answer, but you are still near. The value you got lags by few points.

[Rashakil Fol]

Okay, now I'd really like to see the answer.

[GreenDay2001]

Ok......Its 25.42

Attached the solution.

[Rashakil Fol]

Okay, my answer 24.9 N is still correct; you assumed that g = 10 m/s^2; I assumed 9.80665 m/s^2.

[GreenDay2001]

ok.....sorry for that. I thing in future we must show the value of constants, with the question. I used 10m/s/s 'cause people generally use that to simplify calculations, except for exams :)

Anyway, your turn.

[Rashakil Fol]

Okay, so, from now on let's assume that g = 10 unless stated otherwise.

Here's a problem:

A faucet is turned on; its spout faces straight downwards. It has radius 0.5 cm, and a 0.5 cm radius stream of water flows out of it at a velocity of 2 m/s. What's the radius of the stream 50 cm below the faucet?

[GreenDay2001]

Is the answer 0.37cm. I assumed the flow as streamlined.

[joshSCH]

Ok......Its 25.42

ahh ic, I just gave the frictional force btwn the 3kg and 7kg masses.. Me and Duki just didn't go far enough lol:-/