Physics: Post your doubts here!

[geek101]

Hey guys , check this question real quick.
How is force related with velocity ? What happens to Force if velocity increases or decreases ?

by the formula Power = Force x velocity, P = Fv

this is the derivation in case you havnt come across it,
P = work done / time taken = Fd / t
since d / t = v
then P = Fv

now rearrange to make v or F the subject of the formula, to see the relationship..

v = P / F

and so v is inversely proportional to F. for constant power... If v increases the F decreases and the opp..

 

[axetreme.O]

i discussed this with my teacher yesterday and he said No, the light cannot have a force on any particle. All that it can do is have its light absorbed and emission-ed where its energies are converted from one form to another.

Ask why?-If you can have some more assistance from your teacher.

 

[axetreme.O]

Hey guys , check this question real quick.
How is force related with velocity ? What happens to Force if velocity increases or decreases ?

Try and know the concept of Impulse(a type of force) for this. Impulse is m*v.So if velocity increases with m constant the magnitude of impulse also increases and if velocity decreases the magnitude of impuse decreases too; with mass constant.

 

[raamish]

In qs 7a it is said to distinguish between alpha and beta particle. in the mark scheme answer is written alpha discrete values of speed/energy and B continous spectrum. What does this statment mean. The marking scheme is here: http://www.xtremepapers.com/papers/...and AS Level/Physics (9702)/9702_s08_ms_2.pdf

 

[Sriyog Sharma]

by the formula Power = Force x velocity, P = Fv

this is the derivation in case you havnt come across it,
P = work done / time taken = Fd / t
since d / t = v
then P = Fv

now rearrange to make v or F the subject of the formula, to see the relationship..

v = P / F

and so v is inversely proportional to F. for constant power... If v increases the F decreases and the opp..

I recently came across some question ,and had to deal with this relation. I know power=force*velocity but this question bit confused me . I checked the mark scheme too, didn't help .

I am having problem with the last part.

 

[raamish]

can u upload the mark scheme plzzz

I recently came across some question ,and had to deal with this relation. I know power=force*velocity but this question bit confused me . I checked the mark scheme too, didn't helpView attachment 17362View attachment 17363 .

I am having problem with the last part.

 

[Sriyog Sharma]

Try and know the concept of Impulse(a type of force) for this. Impulse is m*v.So if velocity increases with m constant the magnitude of impulse also increases and if velocity decreases the magnitude of impuse decreases too; with mass constant.

but what do you think about P=F*v??

 

[axetreme.O]

but what do you think about P=F*v??

I believe that if velocity increases the force must increase; take an example of a moving car that hits a tree with 10m/s and other car that hits with 80m/s.It is quite logical that in second case the force will be more as the velocity is more. Hence force should be directly proportional to velocity of an object.

 

[geek101]

I recently came across some question ,and had to deal with this relation. I know power=force*velocity but this question bit confused me . I checked the mark scheme too, didn't helpView attachment 17362View attachment 17363 .

I am having problem with the last part.

what year is that?

 

[Sriyog Sharma]

can u upload the mark scheme plzzz

See the last part, it seems really simple,but i am not getting it!

 

[emkay]

Anyone has the projectile formulas for AS physics ? I would appreciate if yo provide me the formulas of both horizontal and vertical component / help guyss :/

Projectile:
Motion in two dimensions,
v and angle θ with
horizontal, upward is +

x-component → no acceleration
Vx = V cos Ø
x = Vxt = Vt cos Ø

y-component → acceleration is g
Vy = V sin Ø
y = Vyt − ½ gt^2

horizontal range → R =(V^2/g) sin 2Ø
max range at θ=45 deegree.

 

[emkay]

Ask why?-If you can have some more assistance from your teacher.

because it does not have enough mass, and for force mass is a must, since F=m*a. for further detail you need to go deep into quantum of mechanics. but I'll still ask him again on Tuesday!

 

[emkay]

by the formula Power = Force x velocity, P = Fv

this is the derivation in case you havnt come across it,
P = work done / time taken = Fd / t
since d / t = v
then P = Fv

now rearrange to make v or F the subject of the formula, to see the relationship..

v = P / F

and so v is inversely proportional to F. for constant power... If v increases the F decreases and the opp..

I believe that if velocity increases the force must increase; take an example of a moving car that hits a tree with 10m/s and other car that hits with 80m/s.It is quite logical that in second case the force will be more as the velocity is more. Hence force should be directly proportional to velocity of an object.

o.0

 

[geek101]

See the last part, it seems really simple,but i am not getting it!

see here there taking F and V in relation to power.
P is directly proportional to F
P is directly proportional to V

ok if the lorry's speed increases, definitely the resistive forces (air resistance) would increase. now the force and the velocity are both increasing. and both are directly proportional to the Power. so the power will increase. And Power here is needed to overcome the air resis. so it makes sense..that the lorry will need more power now, if the speed it to be kept constant (after the increase)

 

[geek101]

I believe that if velocity increases the force must increase; take an example of a moving car that hits a tree with 10m/s and other car that hits with 80m/s.It is quite logical that in second case the force will be more as the velocity is more. Hence force should be directly proportional to velocity of an object.

what if a car is moving with a velocity and you want to apply a force to stop it....the more the force the lesser the velocity.

 

[Jspake]

Hey guys,
I was solving a vector & moments question as a part of my revision and got stuck somewhere. I really need your help.. some sub-questions are solved (a & b) , please correct me if I'm wrong.
Here's the question (Its kinda long) :

The free-body diagram shows three forces that act on a stone hanging at rest from two strings.

(a) Calculate the horizontal component of the tension in each string. Why should these two components be equal in magnitude?

String 1: =F cosθ = 1 x cos60 =0.5 N
String 2: =F cosθ = 0.58 x cos30 = 0.5 N

The components are equal in magnitude because the stone is at rest and there is no horizontal movement.

(b) Calculate the vertical component of the tension in each string

String 1: F Sin θ = 1 x sin60 = 0.87N
String 2: F Sinθ = 0.58 x sin30 = 0.29N

(c) Use your answer to (b) to calculate the weight of the stone

= 0.87 + 0.29 N
= 1.16N
(Not sure about this answer)

(d) Draw a vector diagram of the forces on the stone. This should be a triangle of forces

I don’t know how to solve this one – please help!

(e) Use your diagram in (d) to calculate the weight of the stone

This one too.. help!!


Waiting for your replies..
Thanks!

 

[messi10]

My doubt is related to the question I attached.

How currents are related in this question. The answer is "I1 + I3 = I2", but can someone please explain according to the law "sum of currents in to the junction equal to out of the junction." How signs are put over here.

Next part: Why e.m.f's are subtracted in this question.. Aren't they to be added?

I am pretty much disappointed from my concepts of Kirchoff's law. Please help me to do this Question (taken from OCT/NOV 2011 - p22).

I'll be your grateful.

 

[geek101]

can someone explain b iii

qp: http://www.xtremepapers.com/papers/...and AS Level/Physics (9702)/9702_w02_qp_2.pdf

ms: http://www.xtremepapers.com/papers/...and AS Level/Physics (9702)/9702_w02_ms_2.pdf

 

[aniroula]

Can any one help me with these questions

May june 11 paper 23
No 3 d(i) and (ii)
No 6 a (iii)
No 5 b (i)

 

[axetreme.O]

what if a car is moving with a velocity and you want to apply a force to stop it....the more the force the lesser the velocity.

the more the force the lesser the velocity..??? whhat?? If a car is moving with a higher velocity you need more force to stop unlike the one that is travelling with lesser velocity.Think of the brakes.If you want to keep the stopping distance same..you have to brake harder for the one that is travelling with a higher velocity.