TrueTears question thread

[TrueTears]

but in circular motion, doesn't acceleration always point towards the centre?

and in projectile motion, acceleration is always down towards the earth ?

[Damo17]

but in circular motion, doesn't acceleration always point towards the centre?

and in projectile motion, acceleration is always down towards the earth ?

I would say it changes direction from south at the top to east and then north and then west as it goes around.

[kamil9876]

You are right about projectile motion, but not about circular motion.

Yes you are right that it's always to the centre, but always to the centre is not the same direction!

Think about it in terms of vectors:



then



So the acceleration is not constant. Constant in magnitude yes, but not constant in direction since this vector changes over t, just like position changes over t.

[kamil9876]

but in circular motion, doesn't acceleration always point towards the centre?

and in projectile motion, acceleration is always down towards the earth ?

I would say it changes direction from south at the top to east and then north and then west as it goes around.

Yep, 'always to the centre' does not mean 'always the same direction' so when it is at the top, the acceleration is south, whereas at the west the acceleration is east. So even tho 'always to the centre' is true doesnt mean 'always the same vector'(direction)

[kaanonball]

but in circular motion, doesn't acceleration always point towards the centre?

and in projectile motion, acceleration is always down towards the earth ?

in projectile motion the Vertical acceleration is due to gravity (9.8m/s/s downwards) i.e. as you said towards the center of the earth but their also exists a Horizontal acceleration which is always 0

[TrueTears]

oh yes stupid me haha

thanks kamil and damo

but in circular motion, doesn't acceleration always point towards the centre?

and in projectile motion, acceleration is always down towards the earth ?

in projectile motion the Vertical acceleration is due to gravity (9.8m/s/s downwards) i.e. as you said towards the center of the earth but their also exists a Horizontal acceleration which is always 0

yeah just didn't include that in my passage

[TrueTears]

Also question 8.11 (structures and material question)

Do you draw the forces which parts of the MACHINE exerts, or the forces that is exerted ON the machine?

for example, if you had a string and 2 people pull on the 2 ends in opposite directions. Then the string would be in tension and there would be forces acting towards the right and left (where the 2 people pulling it), but because of newtons 3rd law, the string is also trying to pull INwards, so what forces do I actually label on this diagram? (Because our teacher stressed that when something is in tension then the material in tension is pulling inwards and if it is in compression then its actually pushing outwards. However, the forces being EXERTED ON the material for tension is 'stretching' it longer and for compression it's 'pushing it inwards'.) So yeah, what forces do I put in here? Thanks

[Mao]

What is the question? what forces are acting on the string? or what forces are exerted by the string?

[TrueTears]

question says: "Draw arrows on the diagram to show which parts of the machine are in tension and which are in compression." How do you interpret that?

[Mao]

question says: "Draw arrows on the diagram to show which parts of the machine are in tension and which are in compression." How do you interpret that?

oh, as in show the forces acting on the cable, supporting frame, etc [so parts in tension have forces acting outwards, parts in compression have forces acting inwards]

[TrueTears]

question says: "Draw arrows on the diagram to show which parts of the machine are in tension and which are in compression." How do you interpret that?

oh, as in show the forces acting on the cable, supporting frame, etc [so parts in tension have forces acting outwards, parts in compression have forces acting inwards]

cool thanks.

[TrueTears]

Structure materials detailed study question: Any help with question 13 would be greatly appreciated XD!

[TrueTears]

And last one question 27

thanks guys

[Mao]

If the truck were to tip, the fulcrum would be at the left support.

The maximum torque by the weight is experienced when the arm is horizontal. Since the truck is required not to tip, we hence have rotational equilibrium:

, where m is the mass of the truck in tonnes

[dejan91]

Hmmm question 13... how do you explain 'feel'?? Well, I'll have a go. And please excuse me if I'm completely wrong
This is assuming stress is loaded at a constant rate:

For a) He would feel a constant increase in length - No sudden changes.
For b) He would feel the line extending minimally for a brief time, then at a quickening rate (reaching a maximum in between the arrows of graph b.), and then once again extending at a depreciating rate.
You can confirm this by considering Young's Modulus, .
From this, . So, a lower value for Youngs modulus, , would result in a greater change in length, . Looking at graph b), it is evident that the lowest value of Youngs modulus occurs between the two arrows, and so the greatest change in length occurs here too.

For c)  He would feel the line change length at an exponential rate.

Now, I'm not sure if you were meant to answer the question in terms of tension or change in length or something else, but I hope this helps