1,000,000 Question Thread :D

[kenhung123]

Thanks for that.

When net force is 0, does the acceleration have to be 0?

[Aden]

Ooooh, THAT question 4 >_>

And yes, but the object can still be moving at a constant speed.

[/0]

Thanks for that.

When net force is 0, does the acceleration have to be 0?

Yes

[kenhung123]

Is this an error in the text?

If I lift a box from the ground at rest which is 10kg, at a constant speed of 2m/s. How much work is done?

[appianway]

There's not an error being done in the text. Think about this. In order to make it travel at a constant speed, the NET force must be 0. There's already a force of around 100 N downwards due to gravitational effects. You therefore have to apply a force of about 100N so that it can travel at a constant speed.

[Aden]

Yeah, there are a few printing errors in that chapter, it is supposed to be:

Also, there is no displacement in your question? Just use

[appianway]

There has to be a displacement if it's moving with a velocity...

[kenhung123]

There's not an error being done in the text. Think about this. In order to make it travel at a constant speed, the NET force must be 0. There's already a force of around 100 N downwards due to gravitational effects. You therefore have to apply a force of about 100N so that it can travel at a constant speed.

Why is there no acceleration at the top and bottom of vertical round pipe?

[m@tty]

Thanks for that.

When net force is 0, does the acceleration have to be 0?

Think

But mass > 0, therefore a must be equal to 0.

[appianway]

There's not an error being done in the text. Think about this. In order to make it travel at a constant speed, the NET force must be 0. There's already a force of around 100 N downwards due to gravitational effects. You therefore have to apply a force of about 100N so that it can travel at a constant speed.

Why is there no acceleration at the top and bottom of vertical round pipe?

Do you mean roller coaster? There can be.

[kenhung123]

Like a perfect semi circular pipe.

[Studyinghard]

Man I am just not getting any of these questions for some reason.

Forces of 12.0 N and 16.0 N act at right angles on a mass of
4.0 kg. What is the acceleration produced by the forces if the mass
is placed:
a) on a smooth surface?
b) on a rough surface where there is a frictional force of 2.0 N
opposing the motion?

But I am going to put my working out and if someone could tell me what I am doing wrong.


Okay so my diagram I drew terribly in paint is up.



Anything wrong there?

If not then I go well I have to find the horizontal component using _{by rope}F_{on boulder} X Cos degrees


_{by rope}F_{on boulder} X Cos degrees
  = 12N x Cos 90^o
  = 0

  = 16N x Cos 90^o
  = 0

So I get 0 which obviously means I am doing something wrong.

[Aden]

I'm guessing that both these forces are pushing against the object at right angles (ie. horizontal push)? If they are pulling instead, then it would move in the opposite direction.

Newton's Second Law is:

Using this, and calling left as positive:
(a)
(left)

(b)
(left)

*Remember though, that the angle is always the angle between the 'applied' force and the 'direction of motion'.

[Studyinghard]

I'm guessing that both these forces are pushing against the object at right angles (ie. horizontal push)? If they are pulling instead, then it would move in the opposite direction.

Newton's Second Law is:

Using this, and calling left as positive:
(a)
(left)

(b)
(left)

*Remember though, that the angle is always the angle between the 'applied' force and the 'direction of motion'.

Well if they are pulling would it look like that the right angles are on the outside? I think they are pulling because the answers in the book are..

and i quote.

[Akirus]

The angle would be the same whether you push or pull, you'd just reverse the signs in your calculations.