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The Physics AS-Level Thread

Reply 1700

Dalek1099

21

Original post by chemistrynerd13

Can someone help me with this question. I don't understand the solution

Attachment not found

What exactly are you stuck on? The question is solved by using the
two conditions necessary for equilibrium:
1. The total moment is 0 - think of a ruler to work out which way the
object would turn under the act of each moment because anticlockwise
and clockwise moments have to have a minus sign with respect to each
other e.g anticlockwise moment - clockwise moment=clockwise moment - anticlockwise moment = 0 or clockwise moment=anticlockwise
moment.
2. The total force is 0 in both horizontal and vertical directions.

When calculating the moment about a point remember that its defined as force x perpendicular distance from point
not just simply force x distance.

This means to calculate the moment you must draw a line from the point to the force that is at right angles to the force - if only a parallel line can be drawn then the perpendicular distance is 0 and so the moment is 0.

If the force acts where you are taking the moments from then the moment is 0 because the perpendicular distance is 0.

I've attached an image to help demonstrate the forces and perpendicular forces from the point to the force relevant for the problem.

(edited 6 years ago)

Reply 1701

Dalek1099

21

Original post by maansari

I need help with this question i dont know how to solve thisIn a film stunt, a car is driven off a cliff with a horizontal velocity of 11.6 ms-1. The cliff face is vertical, and the cliff is 23.6 m high.Calculate the distance in m from the base of the cliff to the point where the car strikes the ground, to 1d.p.

The acceleration from gravity is vertical(downwards) so that the horizontal velocity remains constant and thus the distance=(11.6 ms^-1)*time.

The time is found by using s=ut+1/2at^2 with s=d(after)-d(before)=
0(m)-23.6(m)=-23.6(m) and a=-g=-9.81(ms^-2).

Reply 1702

djm__

1

hey could someone help me out with this question. Why do two wires in a series circuit made of the same material have electrons of the same velocity flowing through them when they are different widths? i get this means that they have the same current but i don't understand it when it comes from the equation I=nqvA. surely this would mean that a greater area A, means a current. thanks :h:

Reply 1703

ryan234

3

Another great website is physicsandmathstutor.com

Original post by djm__

hey could someone help me out with this question. Why do two wires in a series circuit made of the same material have electrons of the same velocity flowing through them when they are different widths? i get this means that they have the same current but i don't understand it when it comes from the equation I=nqvA. surely this would mean that a greater area A, means a current. thanks :h:

I afraid that I may not give you a satisfactory explanation because I don’t really understand your question as they don't seem to be connected. :smile:

Original post by djm__

hey could someone help me out with this question. Why do two wires in a series circuit made of the same material have electrons of the same velocity flowing through them when they are different widths? …

Is your different widths implies different cross-sectional area?

When 2 wires of the same material with different cross-sectional areas are connected, the current is the same but the drift velocity is different. It can be seen from the equation that you quoted

nqv₁A₁ = nqv₂A₂

Both n and q are same. Since A₁ and A₂ are different, v₁and v₂ would be different as well.

Original post by djm__

…i get this means that they have the same current but i don't understand it when it comes from the equation I=nqvA. surely this would mean that a greater area A, means a current. thanks

What do you mean by “…A greater A means a current”?

Reply 1705

Rosy monaghan

4

1.

2.

1

3.

about 2 hours ago

4.

Report post
A high resistance voltmeter records the potential difference across a battery which is connected to a variable resistor of resistance R,

The reading on the voltmeter, V, takes the following values: V=V𝟢 when R=R𝟢 and V=V𝟣 when R=R𝟣,

calculate the internal resistance r,

can anyone do this?

Reply 1706

lolthelol

4

A submarine floats in the ocean with half of its volume submerged. Calculate the mass of water required in the ballast tank in order that it may float completely submerged. The total volume of the submarine is 1200m3. Someone help me work this out as I missed the lesson we covered this. Thanks

Reply 1707

HelloHi.

13

recall that the value of specific latent heat for a substance is different for melting/solidifying and for evaporating/condensing SOMEONE PLEASE HELP ME

Reply 1708

office

6

best way to revise physics for the new alevel course? any good resources/tips please?

Reply 1709

ikrshafiq

10

https://www.thestudentroom.co.uk/showthread.php?t=5300100

guys can you help

Reply 1710

lola tameer

8

could somebody please explain me Q3)d) Where is the force 2.7 on the spring acting and how the spring can not have extension when weight is acting on it. Answers to previous parts are a)500 b)1.3 c)2.7
http://pastpapers.papacambridge.com/..._w17_qp_22.pdf

Reply 1711

Jsjsgga09

7

who is sitting the OCR Physics exams on the 15th May 2018????

Reply 1712

Batman2k1

14

Hey guys, i need huge help

I have a tideous revision method which is; i get a wrong answer from a practise test, mark X, then what i do is, on a new sheet of paper, write the solutions to the question, with parts to help me understand the question. This is a problem because it is too long and i want to know if someone does eomthing better to understand it quickly and just moves on and does other questions...

Reply 1713

cj104

11

Can anyone help me with this please? I have no idea where to even start... What should be the pivot even?

Reply 1714

username3346672

10

Original post by cj104

Can anyone help me with this please? I have no idea where to even start... What should be the pivot even?

Took me about 10 mins to get my head around, only got answer through trial and error by taking pivot about different points, eventually here was my answer:

Take pivot as the tip of the ladder and equations for moments have to be calculated vertically and horizontally.

When you have an equation for each for vertical and horizontal moments, rearrange them both for “0=“ and then equate them.

Rearrange final equation for one of the answers, my answer was A can I check if this is correct? Thanks. 59A9679C-F674-4AC2-8629-47203983C4E9.jpg.jpeg

59A9679C-F674-4AC2-8629-47203983C4E9.jpg.jpeg

Reply 1715

cj104

11

Original post by JR127

Took me about 10 mins to get my head around, only got answer through trial and error by taking pivot about different points, eventually here was my answer:

Take pivot as the tip of the ladder and equations for moments have to be calculated vertically and horizontally.

When you have an equation for each for vertical and horizontal moments, rearrange them both for “0=“ and then equate them.

Rearrange final equation for one of the answers, my answer was A can I check if this is correct? Thanks. 59A9679C-F674-4AC2-8629-47203983C4E9.jpg.jpeg

Yes, it's A. Thank you so much!!! :smile:

Reply 1716

GraftTime

13

Original post by JR127

Took me about 10 mins to get my head around, only got answer through trial and error by taking pivot about different points, eventually here was my answer:

Take pivot as the tip of the ladder and equations for moments have to be calculated vertically and horizontally.

When you have an equation for each for vertical and horizontal moments, rearrange them both for “0=“ and then equate them.

Rearrange final equation for one of the answers, my answer was A can I check if this is correct? Thanks. 59A9679C-F674-4AC2-8629-47203983C4E9.jpg.jpeg

Where does F x 0 come from?