Free body diagram and Newton's law

[kingwinner]

[i noticed that recently some of my posts have been moved to other boards, but this post is definitely related to physics, so I guess I should post it here!]

 

I have just started the "Dynamics" topic in my physics class and I have lost all my memories on this topic. :) I hope someone can answer the following questions to refresh my memory. I really appreciate for your help! ;)

 

1) To draw a free body diagram (FBD) for a car that is slowing down, is it possible too have the magnitude of the applied force < magnitude of the force of friction? e.g. can I draw Fapp=5N, Ff=10N on the FBD?

 

2) Given that the coefficient of static friction = 1.00 and mass = 1.00 kg, the frctional force can be calculated to be 9.8N. If I apply a 5N force to this object, would the frictional force be 9.8N or 5N?

 

3) "The minimum amount of force to move the object in question 2 is 9.8N". I don't understand this statement. If the net force is 0, how can it suddenly start moving at constant velocity from rest? Wouldn't it be staying at rest (instead of starting to move) if exactly 9.8N of force is applied?

 

4) If a ball is thrown to maximum height, would the FBD for it only have the force of gravity? And since the ball isn't moving at max. height, the FBD won't have air resistance, right?

 

5)

-If the bottom string is pulled slowly, the top string will break

-If the bottom string is pulled quickly, the bottom string will break

Why? I was told that this is related to the concept of inertia, but I can't see any connection...can someone explain this, please?

 

6) If a person pulls on a string connected to a mass at rest on the ground at an angle, how is it possible to have the net force equal to 0? The normal force and force of gravity balances out, but there is a vertical component of the applied force. With this extra force, how can the vertical net force be 0?

[Buffy]

Hi kingwinner,

 

We keep movin' yer threads because they're questions from your homework. So they keep gettin' put in the Science Projects and Homework forum. If you want to pose a more *general* question about physics--as opposed to "if a ball is dropped from 9m how many seconds will it take to hit the ground", which is asking for a numeric answer--then feel free to post to the Physics forum or whatever tickles your fancy.

 

We're not all opposed to helping you with your homework, but this is where it goes if you want to get help...

 

Not a science teacher but I play one on Hypography.com,

Buffy