Physics: Post your doubts here!

[Hadi Murtaza]

Projectile me aisa sab ata hain ?

lol i wanted 2 write ( y ) instead of

 

[Thought blocker]

I thought it was answered by Zep.. something Copycat

Wat [/quote]
Zepudee ne wo answer diya thana ?
I saw ur previous deleted post

 

[Hadi Murtaza]

Wat

Zepudee ne wo answer diya thana ?
I saw ur previous deleted post [/quote]
dude Zepudee is da 1 whos asking da questions -_-

 

[Thought blocker]

Zepudee ne wo answer diya thana ?
I saw ur previous deleted post

dude Zepudee is da 1 whos asking da questions -_-[/quote]
Acha... sorry

 

[Hadi Murtaza]

dude Zepudee is da 1 whos asking da questions -_-

Acha... sorry [/quote]
I deleted da old post cuz i qouted my own post by mistake

 

[Thought blocker]

Acha... sorry

I deleted da old post cuz i qouted my own post by mistake[/quote]

 

[Snowysangel]

Which formula could be correct for the speed v of the ocean waves in terms of the density p of sea water, the acceleration of free fall g, the depth of the ocean h and the wavelength, lambda?

 

[Zepudee]

Q.9
Impulse (or change in momentum) = Force * time
Impulse = 60 * 0.5 = 30 Ns

Initial momentum of trolley = 30 kg * 3 m/s= 90 Ns
Impule (or change in mometum) = 30 Ns
So final momentum = 90 - 30 = 60 Ns
Final speed = final momentum/mass

Aww thanks. totally forgot to find the speed!! Thank you so so much!!

 

[Hadi Murtaza]

ur most welkum. btw i did find da speed, check out my post

 

[Zepudee]

Im kindof lousy at explaining dis 1

Initial E = E[x] + E[y]
Final E = E[x] only
So Final E = (1/2) Initial E

Sorry Hadi, but can you please explain a bit more about this?

 

[Zepudee]

ur most welkum. btw i did find da speed, check out my post

Ohhh yeah, haha i mean me

 

[Zepudee]

Q.18
Pressure = F/A = W/A = mg/A = g * m/A
m/A = Pressure/g

Density = m/V = m/A * 1/h
Density * h = m/A
Denisty * h = Pressure/g
Denisty = (Pressure/g) /h
Density = Pressure/(g * h)
Density = 15 200/(10 * .8)
Density = 15 200/8
Density = 1900 kg/m³
Answer: B

Hadi Murtaza Oh ya, why Density=m/A*1/h? Heh heh

 

[Hadi Murtaza]

Sorry Hadi, but can you please explain a bit more about this?

yes ofcourse. dat wuz a crappy explanation anyway.

Vx = V*cos(45) = V * (1/√2) = V/√2
Vy = V*sin(45) = V * (1/√2) = V/√2

E = (1/2) * m * (v)²
E = Ex + Ey

Ex = (1/2) * m * (V/√2)²
Ex = m/2 * V²/2
Ex = mV²/4

Ey = (1/2) * m * (V/√2)²
Ey = m/2 * V²/2
Ey = mV²/4

Initial E = Ex + Ey = (mV²/4) + (mV²/4)
Initial E = mV²/2

^^This is da moment when da object is launched in da air.

At maximum height, vertical velocity becomes 0 which means Vy = 0 , so Ey also becomes 0
Hence
Final E = Ex only
Final E = mV²/4

Now compare Final E wid Initial E.
Final E is 1/2 of Initial E
So answer is 0.5E

 

[Hadi Murtaza]

Hadi Murtaza Oh ya, why Density=m/A*1/h? Heh heh

Volume = length * width * height
length * width = Area = A
So Volume = A * height or A * h

 

[Zepudee]

Volume = length * width * height
length * width = Area = A
So Volume = A * height or A * h

Ah ah i see, hahaha thanks thanks

 

[ShreeyaBeatz]

This is of paper 5
when we throw a magnet in a vertical coil , how to make the speed uniform in all parts of its vertical motion? The markscheme says -
1.Use of short magnet so that v is (nearly) constant
2. Use short/thin coil so that v is (nearly) constant
WHY? HOW?

 

[Champ101]

Yeah, that should be it. There is an alternate method, though, just in case you're interested:

Find the gradients of the steepest line that passes through all the error bars, and the shallowest line that passes through all the error bars.

Suppose they happen to be 5.7 and 4.3 in any units (and the gradient of the best fit is 4.0).

The calculation you carry out = 0.5 * (Gradient of Steepest line - Gradient of shallowest line)

In our example, this is 0.5 * (1.4) = 0.7 (in the relevant units).
So we'll write that the gradient is 4.0 ± 0.7.

The marking scheme from a 2012 October/November paper probably puts this best:

"Uncertainties in Question 2

(c) (iii) Gradient [U2]

Uncertainty = gradient of line of best fit – gradient of worst acceptable line

Uncertainty = ½ (steepest worst line gradient – shallowest worst line gradient)"

So really, either method is accepted as long as you make it clear which one you are using.

Good Luck with all your exams!

thanks a lot man!!!

 

[Jinosupreme]

PAPER5 doubts,
So for question 2, we obtained gradient and y-intercept, the questions after that, are we suppose to use raw gradient and y-intercept in calculations, or the round up gradient and y-intercept? Thanks guys!

 

[Snowysangel]

Which formula could be correct for the speed v of the ocean waves in terms of the density p of sea water, the acceleration of free fall g, the depth of the ocean h and the wavelength, lambda?

This is from paper 1...and the answer is v=underoot (g x lambda)...but HOW?

 

[ShreeyaBeatz]

PAPER5 doubts,
So for question 2, we obtained gradient and y-intercept, the questions after that, are we suppose to use raw gradient and y-intercept in calculations, or the round up gradient and y-intercept? Thanks guys!

Always use raw
And please do help with my question! thanks