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GOTW: Sciene and tech game (Page 7)

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akhl

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akhl

Joined: 30 March 2007

Posts: 5233

Posted: 29 October 2008 at 7:14am | IP Logged
Next question from me: -
 
A book is kept on a table-top, which is horizontal. Coefficient of static friction between the book and the table = 0.2
 
Weight of the book is 10 N. Thus normal force from the table = 10 N.
The book is pushed with a horizontal force of 1 N. What is the magnitude of the force of friction by the table on the book? No need of FBD. Just show the calculations and the final answer.

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_rajnish_

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_rajnish_

Joined: 08 February 2008

Posts: 2510

Posted: 29 October 2008 at 12:53pm | IP Logged
Originally posted by akhl

Next question from me: -
 
A book is kept on a table-top, which is horizontal. Coefficient of static friction between the book and the table = 0.2
 
Weight of the book is 10 N. Thus normal force from the table = 10 N.
The book is pushed with a horizontal force of 1 N. What is the magnitude of the force of friction by the table on the book? No need of FBD. Just show the calculations and the final answer.

Lets calculate

Maximum value of static friction =uN

Where u= coefficient of static friction

             N= Normal reaction

Here u= 0.2 and N=10

So maximum value of static friction=0.2*10= 2N

This value is more than 1N, applied force

So the friction force will adjust itself to 1N and the Book will not move and remain stationary

So value of friction force= 1N and direction opposite to applied force

___________________________________________________________________________________

next question-

what is stepper motor and how it works??





Edited by rajnish_here - 30 October 2008 at 1:55am

akhl

IF-Rockerz

akhl

Joined: 30 March 2007

Posts: 5233

Posted: 29 October 2008 at 9:57pm | IP Logged
Rajnish,
Your answer is perfect. 5 points.

bhopalyellow

Senior Member

bhopalyellow

Joined: 31 May 2008

Posts: 747

Posted: 30 October 2008 at 12:53am | IP Logged

This value is more than 1N, applied force

So the friction force will adjust itself to 1N and the Book will not move and remain stationary

So value of friction force= 1N and direction opposite to applied force

rajnish bhaiya/akhl bhaiya.......plz wud  anyone of u explain this last part of the question...i'm not getting it.....Confused


Edited by bhopalyellow - 30 October 2008 at 2:27am

_rajnish_

IF-Dazzler

_rajnish_

Joined: 08 February 2008

Posts: 2510

Posted: 30 October 2008 at 1:44am | IP Logged
Originally posted by bhopalyellow

This value is more than 1N, applied force

So the friction force will adjust itself to 1N and the Book will not move and remain stationary

So value of friction force= 1N and direction opposite to applied force

rajnish bhaiya/akhl bhaiya.......plz wud  anyone of u explain this last part of the question...i'm not getting it.....Confused
opsOuch by mistake i had written less in place of more so plz edit ur quote
let me explain
static friction has a maximum value. this friction acts when the body is stationary. static friction varies accordind to force applied. unlit maximum value is reach which is uN the value of static friction is equal and opposite to force applied and it keeps the object stationary. when the value of force exeeds this maximum value the static friction changes into kinetic friction whose value is slitely less than maximum static friction and remains equal to ukN(uk=coefficent of kinetic friction).
I think you got it if not then tell i will explain you in detailTongue
 

akhl

IF-Rockerz

akhl

Joined: 30 March 2007

Posts: 5233

Posted: 30 October 2008 at 2:03am | IP Logged
Jasleen,
Maximum value of static friction = coefficient of static friction * normal force
Here coefficient of static friction = 0.2
and normal force = 10 N
Therefore coefficient of static friction * normal force = 0.2 * 10N = 2 N
But note that this is the maximum value of static friction. Actual value is equal to this or less than this. If any less value is enough to stop the book from sliding, then static friction is as much as is needed to stop the book from sliding.
I push the book with 1N. This means that if table applies 1N force in opposite direction, then it is enough to stop the book from sliding. So static friction = 1N.
 
_____________________
Suppose I change the question a little bit.
I push the book with 3N force. Other data remain as earlier. Do you know what will happen in this case? 
Note: This question is not a part of the game. So no points on it. So do not worry whether your answer will be right or wrong. It is only for your learning.


Edited by akhl - 30 October 2008 at 2:27am

bhopalyellow

Senior Member

bhopalyellow

Joined: 31 May 2008

Posts: 747

Posted: 30 October 2008 at 2:27am | IP Logged
thank u rajnish bhaiya and akhl bhaiya....actually i got confused with that word 'less'.....and the 2nd half.....coz when i calculated even i got it correct till 2 N with the same formula...but it's all clear now....thank u both of uBig smile......and i have edited my quote rajnish bhaiya.......waiting for more good ques. from both of u.............Tongue

Edited by bhopalyellow - 30 October 2008 at 2:28am

akhl

IF-Rockerz

akhl

Joined: 30 March 2007

Posts: 5233

Posted: 30 October 2008 at 2:31am | IP Logged
Jaslees,
I edited my explanation and in the end, have added a question. It is only for your learning. Can you tackle that? And also please try answering the following question. This is also not a part of the game but only as learning exercise.
 
A book is kept on the table. Both are moving towards north. Table is moving at 2 m/s and book is moving at 1 m/s. Both these values are relative to ground.
What is the direction of force of friction on the book?

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