Physics: Post your doubts here!

[Thought blocker]

Can someone please help me with this one from May 2013 Paper 11:
18 A wind turbine has blades that sweep an area of 2000m2
. It converts the power available in the
wind to electrical power with an efficiency of 50%.
What is the electrical power generated if the wind speed is 10ms–1? (The density of air is
1.3kgm–3.)
A 130kW B 650kW C 1300kW D 2600kW

P = E/t
P = (1/2mv^2)/t [m = density p * volume V]
P = (1/2pVv^2)/t [Vol = Area A * length s]
P = (1/2pAlv^2)/t [l/t = speed v]
P = 1/2Alv^3

Substitute values, Answer is B.

 

[Thought blocker]

WHY KINETIC ENERGY IS 1/2 mv^2 instead mv^2 ?
The definition of joules, the unit of energy is the 1 J = 1 kg * m^2/v^2.

And that 1 joules is the amount of energy needed for the work done by one newton traveling one meter.

From all this, I got the impression that to get energy, you would have to multiply force times distance. Is work, then just a measurement of energy.

Assuming my first assumption that energy = F * D, lets sat a 5kg object is accelerating towards earth from 20 feet above at 9.8 m/s^2 . To get the force, you would have to do 5 kg * 9m/s^2 Then to get energy, that force times distance. So if it traveled 5 meters. The kinetic energy should be F(5kg * 9.8 m/s^2) * D(5 meters.)

Which would end up being 5kg * 49m^2/s^2


Sooo, can someone explain why ke is 1/2 mv^2 instead of just mv^2.

 

[deathvader]

may june 2008 paper 2 q6 part b how do u solve it ?

 

[Thought blocker]

may june 2008 paper 2 q6 part b how do u solve it ?

PAPER 2 ???????????? SOLVE PAPER 1 BHAI!
Here is your answer
when the powers r in series then we will add their reciprocals n when they r in parallel then we will add their values...
1. there will be no current so no power will generate
2. when S2 is closed then current will choose the low resistance path n will only flow through one heater.. so 1.5kW
3. all of them r closed.. no current is passing through B.. so we will simply add the powers that r in parallel with eachother.. 3 kW
4. the current is passing through A and B... so we will add the reciprocals of the powers n the ans will be 0.75 kW
5. Current is passing through all the heaters so... 0.75 + 1.5 = 2.25 kW

 

[_Ahmad]

9)
answer is B because the ball is falling down with constant acceleration so graph will be an reversed parabola
13)
In order to solve this question, you must imagine three person trying to push an object in any directions. And the minimum resultant force will be when the object is remain at stationary. So at stationary or equilibrium, the resultant force applied by the 3 person will be zero and you can apply the same logic here. 3 forces applied to the object can have a minimum resultant force of 0N.
29)
electron will always move in direction parallel to the direction of the beam. electron repel electron so it would move in opposite direction

for Q9 isn't because of air resistance acceleration will become zero

 

[psychiatrist]

Base unit for Volts

 

[Thought blocker]

Base unit for Volts

Voltage = Power/Current
Power = Energy/Time (Joules/second)
Energy = Force * Distance
Force = Mass * Acceleration (Newton's 2nd law)

=> SI base units of Force: kg m s^(-2)
=> SI base units of Energy: kg m^2 s^(-2)
=> SI base units of Power: kg m^2 s^(-3)
=> SI base units of Voltage: kg m^2 s^(-3) A^(-1)

 

[princeali97]

WHY KINETIC ENERGY IS 1/2 mv^2 instead mv^2 ?
The definition of joules, the unit of energy is the 1 J = 1 kg * m^2/v^2.

And that 1 joules is the amount of energy needed for the work done by one newton traveling one meter.

From all this, I got the impression that to get energy, you would have to multiply force times distance. Is work, then just a measurement of energy.

Assuming my first assumption that energy = F * D, lets sat a 5kg object is accelerating towards earth from 20 feet above at 9.8 m/s^2 . To get the force, you would have to do 5 kg * 9m/s^2 Then to get energy, that force times distance. So if it traveled 5 meters. The kinetic energy should be F(5kg * 9.8 m/s^2) * D(5 meters.)

Which would end up being 5kg * 49m^2/s^2

Sooo, can someone explain why ke is 1/2 mv^2 instead of just mv^2.

Bro i really want to suggest u to stop thinking abt how the formula was derived becoz its not gonna help u now.I dont really want to spend tiime on this sorry.Hope u understand.

 

[Thought blocker]

Bro i really want to suggest u to stop thinking abt how the formula was derived becoz its not gonna help u now.I dont really want to spend tiime on this sorry.Hope u understand.

np

 

[not.maria]

for mj 2011 qp12 q16
why cant we solve this MCQ by using sum of upward forces = sum of downward forces
the examiner report says we have to take moments about point X to get the correct ans.
why?

 

[Thought blocker]

View attachment 44128
for mj 2011 qp12 q16
why cant we solve this MCQ by using sum of upward forces = sum of downward forces
the examiner report says we have to take moments about point X to get the correct ans.
why?

u find the horizontal and vertical components and then use pythogras theorem to find F
so 10 sin 30=5N
10 cos 30=8.66025N
5^2 +8.66025^2=100 root of 100 =10N

 

[Snowysangel]

u find the horizontal and vertical components and then use pythogras theorem to find F
so 10 sin 30=5N
10 cos 30=8.66025N
5^2 +8.66025^2=100 root of 100 =10N

Huh I don't get it. Where does the vertical component of the 10N force act?

 

[Thought blocker]

Huh I don't get it. Where does the vertical component of the 10N force act?

LOL gimme question link

 

[Dr. Seuss]

hi everyone,
here is my question


how do i find the answer?

 

[Snowysangel]

LOL gimme question link

I don't know what year it is so I can't shouldn't the equilibrium of forces equation be applied tho? So that the total magnitude if the forces acting equals to 0....F + Fcos30 + Fsin30 = 10; someone see if it works cause I don't have a calculator on me right now

 

[Thought blocker]

I don't know what year it is so I can't shouldn't the equilibrium of forces equation be applied tho? So that the total magnitude if the forces acting equals to 0....F + Fcos30 + Fsin30 = 10; someone see if it works cause I don't have a calculator on me right now

-_- same goes for me dear! :/

 

[Snowysangel]

hi everyone,
here is my question
View attachment 44135

how do i find the answer?

Percentage uncertainty in L + 2(percentage uncertainty in T)

 

[Dr. Seuss]

oh thanks

 

[RoyalPurple]

74-63-224-172.rotatemyad.com/click.php?aid=861&said=06b_05281514p46&v=15&id=303f1e95923419f4c3082dbd549d4fc0&url=http%3A%2F%2F216.144.227.221%2Fclick.php%3Fkey%3Dc32f16f1fe5e9acbf3c3c0421f8d41318b078834ea2&btn=r&bUrl=http%3A%2F%2Fpapers.xtremepapers.com%2FCIE%2FCambridge%2520International%2520A%2520and%2520AS%2520Level%2FPhysics%2520(9702)%2F9702_s11_qp_11.pdf quest 13 ?

74-63-224-172.rotatemyad.com/click.php?aid=861&said=06b_05281514p46&v=15&id=303f1e95923419f4c3082dbd549d4fc0&url=http%3A%2F%2F216.144.227.221%2Fclick.php%3Fkey%3Dc32f16f1fe5e9acbf3c3c0421f8d41318b078834ea2&btn=r&bUrl=http%3A%2F%2Fpapers.xtremepapers.com%2FCIE%2FCambridge%2520International%2520A%2520and%2520AS%2520Level%2FPhysics%2520(9702)%2F9702_w10_qp_11.pdf

quest 5

74-63-224-172.rotatemyad.com/click.php?aid=861&said=06b_05281514p46&v=15&id=303f1e95923419f4c3082dbd549d4fc0&url=http%3A%2F%2F216.144.227.221%2Fclick.php%3Fkey%3Dc32f16f1fe5e9acbf3c3c0421f8d41318b078834ea2&btn=r&bUrl=http%3A%2F%2Fpapers.xtremepapers.com%2FCIE%2FCambridge%2520International%2520A%2520and%2520AS%2520Level%2FPhysics%2520(9702)%2F9702_w11_qp_11.pdf
ques 16


help please thnx

 

[not.maria]

u find thehorizontal and vertical components and then use pythogras theorem to find F
so 10 sin 30=5N
10 cos 30=8.66025N
5^2 +8.66025^2=100 root of 100 =10N

how is the vertical component 10sin 30?