I am calculating the forces on String cheese with net force = 0

[rgtr]

Homework Statement

Example 2: String cheese A wedge of cheese is suspended at rest by two strings which exert forces of magnitude F1 and f2 as seen below. There is also a downward force of gravity on the cheese of magnitude 20 N What is the magnitude of the force F1? What is the magnitude of the force F2?

Relevant Equations

$f = ma$

Here is the link to the question.

https://www.khanacademy.org/science...s-laws-of-motion/a/what-is-Newtons-second-law

What is the magnitude of the force F1 ?

What is the magnitude of the force F2 ?





Here is my drawing I made At this step I am lost.
$ay = (sigmaF1sin60) -20 N$
Shouldn't ay be ax?

 

[haruspex]

Shouldn't ay be ax?

Why? The 20N is a vertical force, and $F_1\sin(60°)$ is the vertical component of $F_1$.

 

[rgtr]

Are you saying o or F1Y = 20N? I don't understand why. Can someone explain?

 

[haruspex]

Are you saying o or F1Y = 20N? I don't understand why. Can someone explain?

What is the net vertical force on the wedge?

 

[rgtr]

Sorry I used a old account to originally respond. The answer is the net force is 0.

 

[haruspex]

Sorry I used a old account to originally respond. The answer is the net force is 0.

Yes, but what vertical forces on it sum to that?

 

[Lnewqban]

Are you saying o or F1Y = 20N? I don't understand why. Can someone explain?

That wedge of cheese is hanging at rest, according to the problem.
Therefore, forces in all directions cancel each other.
If you define axes x and y as to be aligned with F2 and F4, then you need to decompose F1 in its projections on each of those axes: F1x and F1y.

You should remove that F3 from your schematic, since it does not exist.

 

[rgtr]

How can you ignore F3? It can range from 0-20N depending on F1Y. F1Y can also range from 0-20N depending on F3.

 

[Steve4Physics]

How can you ignore F3? It can range from 0-20N depending on F1Y. F1Y can also range from 0-20N depending on F3.

The cheese is not resting on a horizontal surface so there is no upwards normal reaction force (unlike a piece of cheese on a table foe example).

There is no vertical string, so there is no upwards pull from the tension a vertical string.

So there is no upwards force, F3, acting on the piece of cheese. F3 should be removed.

There are 3 forces on the cheese:
F1 - the pull (tension) of the right-hand string on the cheese, at 60º to the horizontal;
F2 - the pull (tension) of the left-hand string – horizontally to the left;
20N - the weight of the cheese (the downwards pull of gravity)

If you think there is another force, F3, what is producing this force?

Also, what type of cheese is it?

 

[rgtr]

Thanks I get it now.
The cheese is Gouda.

Also in Newtonian physics when switching frames does acceleration switch like constant velocity?

 

[jtbell]

When I saw the title of this thread, I thought, "gee, I don't remember ever seeing a physics problem about string cheese."

 

[Lnewqban]

... Also in Newtonian physics when switching frames does acceleration switch like constant velocity?

Could you mention an example of switching frames?

 

[rgtr]

Imagine I have a stationary person called A. And a person who running at an accelerating rate called B.
If I switch to B's frame does A accelerate the same amount as B in A's frame just the opposite direction?

Sorry this is a little wordy.

 

[haruspex]

Imagine I have a stationary person called A. And a person who running at an accelerating rate called B.
If I switch to B's frame does A accelerate the same amount as B in A's frame just the opposite direction?

Sorry this is a little wordy.

Yes.