Vectors question

Original post by Kolasinac138

Hey, I came across this vectors question in a paper, and for part 1) c) i) I was wondering why you add the vector to the left, not the right, of the 16 ms arrow?

http://theallpapers.com/papers/CIE/Pre-U/Physics%20(9792)/9792_s11_qp_2.pdf

Thanks.

Where does it state you have to "add the vector to the left"?

Reply 3

OP

Original post by Stonebridge

Where does it state you have to "add the vector to the left"?

In the markscheme, here:

http://theallpapers.com/papers/CIE/Pre-U/Physics%20(9792)/9792_s11_ms_2.pdf

Reply 4

Because to find change in velocity you have to subtract the initial velocity u from the final velocity v.
To do this you reverse the initial velocity (makes it -u) and then add to v making it v + (-u) = v-u
On the vector diagram you do this by starting the second vector at the tail end of the first vector and not the head. If you were to combine the vectors at the head of the first you would be adding and not subtracting.

Reply 5

OP

Original post by Stonebridge

Because to find change in velocity you have to subtract the initial velocity u from the final velocity v.
To do this you reverse the initial velocity (makes it -u) and then add to v making it v + (-u) = v-u
On the vector diagram you do this by starting the second vector at the tail end of the first vector and not the head. If you were to combine the vectors at the head of the first you would be adding and not subtracting.

I see, thanks. What situation would you put it on the right then? If he gainsa southward velocity of 12?

Reply 6

Original post by Kolasinac138

I see, thanks. What situation would you put it on the right then? If he gainsa southward velocity of 12?

You place the arrows head to tail when you add them.
So if you were to add the final velocity to the initial you would place the 2nd velocity tail to start at the head of the 1st.
You would do that in a question like:

A man is on a boat travelling due east at 16m/s and he walks due south across the boat at 12 m/s. What is his resultant velocity. This is when you vectorially add velocities. I'm sure you've done this before.

Reply 7

OP

Original post by Stonebridge

You place the arrows head to tail when you add them.
So if you were to add the final velocity to the initial you would place the 2nd velocity tail to start at the head of the 1st.
You would do that in a question like:

A man is on a boat travelling due east at 16m/s and he walks due south across the boat at 12 m/s. What is his resultant velocity. This is when you vectorially add velocities. I'm sure you've done this before.

Thanks. Can I further ask, would a compressive stress graph look different to a tensile one?

Reply 8

Original post by Kolasinac138

Thanks. Can I further ask, would a compressive stress graph look different to a tensile one?

Depends on the shape and nature of the material as some will stretch but not compress.
Assuming both are possible and you stay within the elastic limit of the material, then yes. The graphs will have the same form but obviously the direction of the strain is opposite in compression.
Within the material it's the difference between stretching the interatomic bonds or compressing them.

Reply 9

OP

Original post by Stonebridge

Depends on the shape and nature of the material as some will stretch but not compress.
Assuming both are possible and you stay within the elastic limit of the material, then yes. The graphs will have the same form but obviously the direction of the strain is opposite in compression.
Within the material it's the difference between stretching the interatomic bonds or compressing them.

Would it be a graph of 'negative extension'?

Reply 10