Physics: Post your doubts here!

[waleedsmz]

Q. How much the momentum of a body would increase by increasing the K.E by 300%?...........the ans is 100%.....but could someone please explain to me the method to solve this question.....would appreciate it a lot!

K.E.(original) = 0.5mv^2... let it be 0.5, and the new one be 2
0.5mv^2 = 0.5, mv^2=1, v=root(1/m)
similarly, new v = root(4/m)
mv ( original ) = 1 root(m)
mv ( new ) = 2 root(m)
The new one is double the old one and therefore the increase is 100%.

Notice that the more "formal" way of solving this question is calling the constant ( 0.5 ) that we given to the kinetic energy "k" for example, new one would be "4k". It would lead to the same answer but I guess the other method looks easier.

 

[Nabeel.Ahmad]

What's the Best book for Physics?

 

[Haider Nisar]

hello ppl!i need some help regarding about the total marks for As physics examination!and how many marks are required to bring an A in As!and i am done with my physics 2013 As examination!i found p1 very hard!but what abt u guyz?!!

 

[Student12]

Hey need help !
I want to give a 3rd A-level so i wanted to ask. I've done Biology & Chemistry and AS AICT.
shall i do Physics or math? Which is an easier subject that will allow me to prepare in 3 months?

Help answer ASAP!

 

[waleedsmz]

Hey need help !

I want to give a 3rd A-level so i wanted to ask. I've done Biology & Chemistry and AS AICT.
shall i do Physics or math? Which is an easier subject that will allow me to prepare in 3 months?
Help answer ASAP!

Neither is easy. The problem with mathematics however is the very low gradient. I remember you could lose like 80 marks in physics and still have an A*. Maths gradient was about 35 if I remember. I'm not quiet sure though. I took both ALevels and my opinion is that physics would be a better choice. Go with what you love, it always works .

 

[Umar Zain]

Answer this question yo people of the world!!!

 

[SilverCrest]

Answer this question yo people of the world!!!

Where did you get this question from??
The answer seems to be B
At time t=0
air resistance zero as the velocity is zero
remember air resistance is dependent on velocity.the greater the velocity the greater the air resistance.
anyway the body's velocity increases till T so air resistance should also increase.
Before T is reached the air resistance gradually increases at a decreasing rate.This is because the velocity is increasing at a decreasing rate.
after T the velocity becomes constant so air resistance also becomes constant

 

[Umar Zain]

Where did you get this question from??
The answer seems to be B
At time t=0
air resistance zero as the velocity is zero
remember air resistance is dependent on velocity.the greater the velocity the greater the air resistance.
anyway the body's velocity increases till T so air resistance should also increase.
Before T is reached the air resistance gradually increases at a decreasing rate.This is because the velocity is increasing at a decreasing rate.
after T the velocity becomes constant so air resistance also becomes constant

Physics M/J paper_12 2013
Yes I agree too, I'm just curious about the 'increase with increasing rate' near the origin region. I think it's because at that region air resistance isn't so significant yet. Since a=(v^2)/2s & F=ma, whereby aceleration is constant (gravity)...shape of graph should show increasing slope until at some point air resistance is large enough to affect the motion.

 

[Hemdon]

Assalamuailkum Everyone.....can someone tell me SI base units of Power(frm May/June 2013 22)....the answer I am getting is Nms^-1 ....is this correct?? Also.....There is a question about Radioactivity in an aplpha particle...(9702/22/M/J/13 Q 7 a ii).....Explain why the mass seems not to be conserved in the reaction...this question bugs me bcoz everywhere i read it said that...
Total energy (rest mass energy plus kinetic energy)
Number of nucleons
Momentum
Charge
are conserved....please help me out!!!

 

[AbbbbY]

Assalamuailkum Everyone.....can someone tell me SI base units of Power(frm May/June 2013 22)....the answer I am getting is Nms^-1 ....is this correct?? Also.....There is a question about Radioactivity in an aplpha particle...(9702/22/M/J/13 Q 7 a ii).....Explain why the mass seems not to be conserved in the reaction...this question bugs me bcoz everywhere i read it said that...
Total energy (rest mass energy plus kinetic energy)
Number of nucleons
Momentum
Charge
are conserved....please help me out!!!

Power = Work / time
Work = Fd

F= N
d= m
time = s

Nm/s (or Nms^-1)

About radioactivity, Sorry. Haven't done that yet.

 

[RadzMau]

Hi! I need help pls!
The question is: "Why does the moon not fall and hit the earth?"

 

[AbbbbY]

Hi! I need help pls!
The question is: "Why does the moon not fall and hit the earth?"

Due to the gravity b/w them (GMm/r^2 recap?)

 

[Masoom Gilani]

Pleaseee Help!
There is a point along the line joining the centres of the Earth and the moon where their combined gravitational field strength is zero. is this point closer to EARTH or the the moon? Calculate how far it is from the centre of the earth.

 

[Pradeep Adhikari]

Please, i want help for Waves, Diffraction, Interference, Diffraction Grating and Stationary waves. please,please, please HELP!

 

[RadzMau]

Hi! I need help pls!
My question is:
'Assuming that the Moon travels at a a constant speed around the Earth at the centre of the circle, calculate the acceleration of the Moon.'

 

[Pradeep Adhikari]

Friend, Read this, it may be more than useful to you.....
http://www.physicsclassroom.com/Class/vectors/

 

[Pradeep Adhikari]

Please Help GUYS............................................How can uranium exist in many isotopes?

 

[Minato112]

Hi! I need help pls!
The question is: "Why does the moon not fall and hit the earth?"

The gravitational force of the earth provides the centripetal force for the circular motion of the earth. Thus the moon continues in its state to motion instead of colliding with the earth

 

[Hemdon]

hi guys, question is " use kinetic model to explain the pressure exerted by a gas"...4 marks....and I wrote" A gas exerts pressure on any surface that comes into contact. There are 2 factors that must be taken into consideration, the force of the particle or atom at which it exerts the walls of the container, and the mass of the particle. The kinetic model states that the rate of the fore applied on the wall of the container, and the particle must be equal, resulting in a constant pressure throughout." is this correct, because i feel something is irrelevant and im missing some details, if u can help me out I'll be very grateful. fell free to tell me and correct me thanks

 

[Minato112]

hi guys, question is " use kinetic model to explain the pressure exerted by a gas"...4 marks....and I wrote" A gas exerts pressure on any surface that comes into contact. There are 2 factors that must be taken into consideration, the force of the particle or atom at which it exerts the walls of the container, and the mass of the particle. The kinetic model states that the rate of the fore applied on the wall of the container, and the particle must be equal, resulting in a constant pressure throughout." is this correct, because i feel something is irrelevant and im missing some details, if u can help me out I'll be very grateful. fell free to tell me and correct me thanks

Well here as I would have answered it : Consider a gas enclosed in a cylinder. The gas molecules move randomly throughout the cylinder and collide with the walls of the cylinder, thereby exerting a force on the cylinder. As pressure is defined as the force acting normally per unit area, upon collisions, the molecules exert a pressure on the walls of the cylinder.

Still, if anyone else has a suggestion, please notify. Hope this helps