# Posts by Elena

Total # Posts: 4,389

**Physics**

t₁=250/9 – 250/7 = 63.5 s t₂ = 500/8 = 62.5 s Δt=t₁-t₂=63.5 – 62.5 =1 s.

*April 30, 2013*

**physics**

mgh= mv²/2 v=sqrt(2gh)

*April 29, 2013*

**physics**

Work/time = Power = Force x speed The force is exerted on the bicycle to maintain the constant speed is F=P/v=400/10 = 40 N

*April 29, 2013*

**physics**

v=const => net force =0

*April 29, 2013*

**physics**

centripetal acceleration a= v²/R= = 4/0.5=8 m/s² centripetal force F= mv²/R= =0.05•4/0.5=0.4 m/s²

*April 29, 2013*

**physics**

centripetal acceleration a= mv²/R= =0.05•4/0.5=0.4 m/s²

*April 29, 2013*

**Physics**

Pb = lead

*April 29, 2013*

**physics**

Please can you tell the numerical value

*April 29, 2013*

**physics**

Tsinθ = mv²/R Tcosθ = mg tanθ=v²/Rg

*April 29, 2013*

**physics**

ma = Tsinθ mg= Tcosθ a/g =tanθ => a=g• tanθ

*April 29, 2013*

**Physics**

L=2.51•10⁻⁶ H x=1.17 m z=? L=μ₀N²A/z N=x/2πr => r= x/2πN => A=πr²=πx²/4π²N² L=μ₀N²A/z= μ₀N²πx²/4π²N²z= = μ₀x²/4z z= &#...

*April 28, 2013*

**chem (boyles and charles law)**

p₁ =1.2 atm = 121590 Pa V₁= 1 L=10⁻³ m³ V₂=0.5•10⁻³ m³ p₁V₁=p₂V₂ p₂=p₁V₁/V₂

*April 28, 2013*

**CRC**

p₂=p₁T₂/T₁ p₁=675 torr = 89992.35 Pa T ₁=273+28 =301 K T₂ = 273+ 91= 364 K

*April 28, 2013*

**Physics**

E₃ = - E₁/n²= - 24.8/9 = - 2.76 eV

*April 28, 2013*

**Physics**

covalent bond

*April 28, 2013*

**Physics**

T•sin60•L=2450•sin30•0.39L +5000•sin30•L T•sin60=(2450•0.39 +5000)•sin30 T=(2450•0.39 +5000)•sin30/sin60=...

*April 28, 2013*

**physics**

mv=(m+M)u u =mv/(m+M), (m+M)u²/2=(m+M)gh. u=sqrt(2gh). mv/(m+M)= sqrt(2gh) v= (m+M)•sqrt(2gh)/m

*April 28, 2013*

**Physical Science**

#4

*April 28, 2013*

**chem (boyles and charles law)**

T₂=V₂T₁/V₁

*April 28, 2013*

**chem. mix of boyles and charles law**

V₂=T₂V₁/T₁ 1 atm = 101325 Pa 1 L = 10⁻³ m³

*April 28, 2013*

**chemistry (charles law)**

V₂=T₂V₁/T₁ T₁=303 K T₂=273 K

*April 28, 2013*

**chemistry (charles law)**

V₂=T₂V₁/T₁

*April 28, 2013*

**physics**

Given data: 1st rod: L₁, T₁, x₁, a => A₁=a²; 2nd rod: L₂, T₂, x₂, d => A₂= πd²/4; Hook’s Law for rods: σ=Eε T/A = E•x/L, 1st rod: T₁/a²= E•x₁/L₁, 2nd rod: 4T&#...

*April 28, 2013*

**Science**

m=D•V

*April 28, 2013*

**Physics**

m=39.0 kg s=4.5 m, F=135 N, μ=0.3 (a) W(F) = Fs (b) ΔU= W(fr) = μmgs (c) W(N) = 0 (d) W(mg) = 0 (e) KE=W(F) –W(fr) =Fs - μmgs (f) KE=mv²/2 v= sqrt(2•KE/m)

*April 28, 2013*

**physics**

The sums of torques respectively the edges of the board are: W•x-400•2 = 0 W• (2-x) -700•2=0 W•x=800 2W-W•x -1400 = 0 2W-800-1400=0 W=1100 N x=800/W =0.73 m

*April 28, 2013*

**physical science**

(A)tetrahedral This distorted tetrahedral arrangement is call bent. http://www.ausetute.com.au/shapemol.html

*April 28, 2013*

**physics**

h=s•sinα=v•t•sinα=1.5•21•sin30=15.75 m

*April 27, 2013*

**physics**

p=sqrt{p(x)²+p(y)²} = = sqrt{(10•9) ² +(20•12)²}=256.32 kg•m/s v= p/(m₁+m₂) =256.32/30 =8.54 m/s

*April 27, 2013*

**physics**

k =9•10⁹ N•m²/C² r=0.18 m q₁= 5•10⁻⁹ C q₂ = - 2•10⁻⁹ C PE= k•q₁•q₂/r = ...

*April 27, 2013*

**physics**

φ =198t-24t²-2t³ (a) ω=dφ/dt=198 -48t-6t², ω=0 => 198 -48t-6t²=0, 6t²+48t-198=0, t²+8t – 33 =0, t= -4±√(16+33 ) =-4±7, t=-11 (impossible), t=3 s. (b) ε=dω/dt= - 48 -12t. t=3 => ε=-...

*April 27, 2013*

**Physics**

F=qE=eE => E=F/e=3•10⁻¹⁵/1.6•10⁻¹⁹= 1.875•10⁴ N E=Δφ/Δx= Δφ/d => Δφ=Ed=1.875•10⁴•0.2=3.75•10³ V

*April 27, 2013*

**Physics**

mg=kx x=mg/k=2.35•9.8/1.64•10³=0.014 m

*April 26, 2013*

**Physics**

F=k•q₁•q₂/r², k =9•10⁹ N•m²/C², q₂ = F•r²/k•q₁ = 1.8•0.3²/9•10⁹•6•10⁻⁶ = =3•10⁻⁶ C = 3 μC Due to the attraction of the charges q&#...

*April 26, 2013*

**Physics**

F=k•q₁•q₂/r²= k•q²/r² q=sqrt{ F•r²/k}=sqrt{7•10⁻⁹•(3.2•10⁻¹⁰)²/9•10⁹}=2.82•10⁻¹⁸C

*April 26, 2013*

**Physics-- please help me finish!!**

m₂g=kx k= m₂g/x=0.363•9.8/0.026 = 136.8 N/mþ T=2π•sqrt(m₁/k) = =2π•sqrt(1.4/136.8)=0.64 s

*April 26, 2013*

**physics**

L=Iω=mR²ω =0.5•1.45²•1.5 = 0.29 kg•²/s

*April 26, 2013*

**physics**

fluorine gas F₂=> μ = 36 g/mol =36•10⁻³ kg/mol, m= 0.076 kg, V=1.5 L = 1.5•10⁻³ m³, t= -37℃ = 236 K, pV=mRT/ μ => p =mRT/ Vμ =0.076•8.31•236/1.5•10⁻³•36•10⁻³= =...

*April 26, 2013*

**Physics SI unit**

Newton

*April 25, 2013*

**physics**

F₁=mv²/R₁ F₂=mv²/R₂=mv²/2R₁=F₁/2

*April 25, 2013*

**Physics**

B=sqrt{B(y)²+B(z)²} = =sqrt{0.5²+0.67²} = 0.836 T, F=qvBsinα, sinα=1, F=qvB=31•10⁻⁶•62•0.836=1.6•10⁻³ N. Vector B makes an angle β with z-axis: tanβ =B(y)/B(z) =0.5/0.67=0.746, β=36.7° ...

*April 25, 2013*

**physics - stopping distance**

The reaction time is t =x/v=7.5/10 = 15/20 =22.5/30 = 0.75 s. The reaction distance for v=25 m/s is x=vt=25•0.75 = 18.75 m. The acceleration is a=v²/2s=10²/2•5=20²/2•20=30²/2•45=10 m/s² The breaking distance for v=25 m/s is s= v&#...

*April 25, 2013*

**physics**

F=ILB B=F/IL

*April 25, 2013*

**physics**

mgh=mv^2/2, v=sqrt(2gh) = ...

*April 25, 2013*

**physics**

F=qvB =evB v=F/eB=...

*April 25, 2013*

**physics**

engine’s eﬃciency=A/Q =417/848=0.49 or 49%

*April 25, 2013*

**Physics**

A) L=λ/2=v/2f B) L=λ/4=v/4f v is the speed of sound

*April 25, 2013*

**Physics**

φ=ω₀t±εt²/2 ω=ω₀±εt ω=2πn ω₀=2πn₀=0 φ=εt²/2 2πn= εt ε=2πn/t φ=εt²/2=2πn t²/2t= πn t=3.14•30•5=...(rad)

*April 24, 2013*

**Physics**

mg(H+h)=mv²/2 v = sqrt{2g(H+h)}

*April 23, 2013*

**Physics**

p=ρgh+p₀ = 1025•9.8•10300+101325 =103564825 Pa F=pA=pπr²=103564825•π•0.13²=5.5•10⁶ N

*April 23, 2013*

**Science/DUE TODAY**

http://wiki.answers.com/Q/What_3_changes_polar_bears_would_need_to_change_to_live_in_the_desert

*April 23, 2013*

**Quantum Physics**

1/λ =R(1/n² - 1/m²) = =1.1•10⁵(1/1²-1/∞) λ = 9.1•10⁻⁶ m

*April 22, 2013*

**Math**

10/(3x) + 4/3 = (7+x)/2x 20+8x=21+3x 5x=1 x=1/5

*April 22, 2013*

**Physics Eletric fields and coulomb's law)**

E=ke/r², r=sqrt(ke/E) = = sqrt(9•10⁹•1.6•10⁻¹⁹/2.02•10⁻⁷)= =8.44•10⁻²m

*April 22, 2013*

**Math PLEASE HELP!**

What is the base of your logarithms? If it is common logarithm logx=log₁₀x=3.5829 => x=10³•⁵⁸²⁹=3827.366 If it is binary logarithm logx=log ₂x=3.5829 x=2³•⁵⁸²⁹=11.983. If it is natural ...

*April 22, 2013*

**physics**

The gravitational constant G =6.67•10⁻¹¹ N•m²/kg², h=100000 m m=1040 kg Earth’s mass is M = 5.98•10²⁴kg, Earth’s radius is R = 6.37 •10⁶ m. (a) F =G•m •M/(R+h)² (b) a= G• M/(R+h)²...

*April 22, 2013*

**science**

http://en.wikipedia.org/wiki/Thermal_conduction

*April 22, 2013*

**Physics**

B=μ₀I/2πb=1.25664•10⁻⁶•1.24/2π•0.436 =5.69•10⁻⁷ T

*April 22, 2013*

**physics**

F=qE=eE=1.6•10⁻¹⁹•341•10⁵=5.456•10⁻¹² N

*April 22, 2013*

**Physics**

cosα=1, ℇ=ΔΦ/Δt = N•Δ(B•Acosα)/Δt= =N•A•ΔB/Δt, ℇ=I•R, N•A•ΔB/Δt= I•R, I= N•A•ΔB/Δt•R= =347•0.28•2.4/0.31•49 = 15.35 A

*April 22, 2013*

**physics**

cosα=1 ℇ=ΔΦ/Δt = N•Δ(B•Acosα)/ Δt= =N•A•ΔB/Δt ℇ=I•R N•A•ΔB/Δt= I•R I= N•A•ΔB/Δt•R= ...

*April 22, 2013*

**PHYSICS!!!!...PLEASE HELP**

v=const => mgsinα=F(fr) = μN= μmgcosα sinα= μcosα μ=tanα

*April 22, 2013*

**physics**

mgh=kx²/2 x=sqrt(2mgh/k)

*April 21, 2013*

**Science**

An ion is an atom or molecule in which the total number of electrons is not equal to the total number of protons, giving the atom a net positive or negative electrical charge.

*April 21, 2013*

**Physics**

The object located between F and 2F => the image will be located beyond the 2F point on the other side of the lens. It is real, inverted and its dimension is larger than the object demension. d₀ - object distance d₁ - image distance f- focal lenth 1/d₀ +1/...

*April 21, 2013*

**Physics *Electrical Scientist* please help me!!!**

http://www.tutorvista.com/science/jj-thomson-atomic-theory-0 http://en.wikipedia.org/wiki/Cathode_ray_tube

*April 20, 2013*

**calculus**

t=∛x =x^(1/3) => y=3x^5 = 3x^(5/3). dy/dx =3•(5/3)•x^(2/3) = =5 •125^(2/3)=525=125

*April 20, 2013*

**Physics**

d₀ - object distance d₁ - image distance f- focal lenth 1/d₀ +1/d₁ =1/f, 1/d₁ =1/f - 1/d₀ = = (d₀-f)/ d₀•f, d₁=d₀•f/(d₀-f)= =0.4•0.15/(0.4-0.15)=0.24 m, 0.03/0.4 =h/ d₁ , h= d₁•0....

*April 20, 2013*

**Physics**

mgsinα=F(fr) = μN= μmgcosα sinα= μcosα μ=tanα

*April 20, 2013*

**calculus**

s= 189t- t³ v=ds/dt = 189-3t² t=0 = > v=189 m/s. 189-3t² = 0 t=√(189/3) =√63 = 7.94 s. s=189 t- t³= =189(7.94) -7.94³=1000.1 m a=dv/dt =d(189-3t²)/dt= - 6t t=8 => a= - 6•8 = - 48 m/s²

*April 20, 2013*

**physics**

I=2mR²/5 ω=2π/T KE= Iω²/2

*April 20, 2013*

**Physics**

m₁gh= m₁v₁₀²/2 => v₁₀=sqrt(2gh) m₂gh= m₂v₂₀²/2 => v₂₀ =sqrt(2gh) m₁v₁₀ - m₂v₂₀= - m₁v₁ + m₂v₂ v₁= {-2m₂v₂₀...

*April 20, 2013*

**Physics**

C)λ, ν, and 100E

*April 20, 2013*

**calculus (gr 12)**

f(x) = 2x³+4x²-5x+8 f′(x) =6x²+8x-5 f′(-2) = 2(-4) ² +8(-2) -5 = 11

*April 19, 2013*

**calculus**

f(x) =x⁴-3x f′(x) = 4x³ -3 => f′(3) = 4•3³ -3= 105

*April 19, 2013*

**calculus (gr 12)**

s= 189t- t³ v=ds/dt = 189-3t² t=0 = > v=189 m/s. 189-3t² = 0 t=√(189/3) =√63 = 7.94 s. s=189 t- t³= =189(7.94) -7.94³=1000.1 m a=dv/dt =d(189-3t²)/dt= - 6t t=8 => a= - 6•8 = - 48 m/s²

*April 19, 2013*

**physics**

X: ma=Fcosα-F(fr) Y: 0=-mg+N+Fsinα =>N=mg-Fsinα F(fr) = μN=μ(mg-Fsinα) ma= Fcosα- μ(mg-Fsinα) a = { Fcosα- μ(mg-Fsinα)}/m

*April 19, 2013*

**physics**

S=(v-v₀)•t=(2-1) •3•60= 180 m

*April 19, 2013*

**physics**

F₁=k•q₁•q₂/r₁², F₂=k•q₁•q₂/r₂², F₁/F₂=k•q₁•q₂•r₂² / k•q₁•q₂•r₁², F₂= F₁• r₁²/r &#...

*April 19, 2013*

**Physics**

T₁=2πsqrt(m₁/k) T₂=2πsqrt(m₂/k) T₁/T₂=sqrt{m₁/m₂} T₂=T₁/sqrt{m₁/m₂}= 2.8 s

*April 19, 2013*

**Physics**

λ=v/f =3•10⁸/6•10¹⁶=5•10⁻⁹ m

*April 19, 2013*

**Literature ?! Check my answers?**

CCB! just took test too!

*April 17, 2013*

**Physics :)**

Angular acceleration= torque/moment of inertia

*April 13, 2013*

**physics**

T + mg = mv²/R => T = m (v²/R -g)

*April 13, 2013*

**physics**

Tsin(α/2)=kq²/{2Lsin(α/2)}², Tcos(α/2)=mg. tan(α/2)= kq²/mg{2Lsin(α/2)}², m= kq²/g{2Lsin(α/2)}²•tan(α/2)=...

*April 13, 2013*

**physics**

m₁gh₁ =mv²/2, v=sqrt(2gh₁)=… m₁v=(m₁+m₂)u, u= m₁v/(m₁+m₂)=.. . (m₁+m₂)u²/2=(m₁+m₂)gh₂, h₂=(m₁+m₂)u²/2(m₁+m₂)=..

*April 13, 2013*

**physics**

h=gt²/2 t=sqrt(2h/g) =sqrt(2•200/9.8)=6.39 s

*April 12, 2013*

**Physics**

a) density b) acceleration c) - d) - e) refractive index f)capacity g)resistance h) pressure

*April 11, 2013*

**physics**

a=F/m=90/(40+3) = 2.1 m/s2

*April 11, 2013*

**physics**

ma=F(fr), mv²/R =μmg, v=sqrt(μRg) = sqrt(0.63•39.6•9.8)= …

*April 11, 2013*

**physics**

F(x) =-F(1x) +F(2x)+F(3x) – F(4x) = =(G•m₅•cos45°•2/s√2)•(-m₁+m₂+m₃-m₄)=... F(y) = F(1y) +F(2y)-F(3y) – F(4y) = =(G•m₅•sin45°•2/s√2)•( m₁+m₂-m₃-m₄...

*April 11, 2013*

**Physics!! HELP**

λ=2•2.5=5 m s=14•5=70 m v=s/t=70/15=4.67 m/s

*April 11, 2013*

**Physics**

An object is placed 11 cm in front of a concave mirror whose focal length is 23 cm. The object is 3.6 cm tall. Determine (a) the location of the image, taking a real image as a positive value and a virtual image as a negative value. (b) Determine the height of the image, where...

*April 11, 2013*

**Physics Hear**

1) Q=c•m•ΔT=4183•10•(100-20)=3346400 J 2) Q=Lm = 2260000•0.01 = 22600 J 3) Q= Q₁+Q₂+Q₃= c₁•m•ΔT₁+rm+ c₂•m•ΔT₂= =2060•3•7+ 335000•3+4183•3•25 = =43260...

*April 11, 2013*

**physics**

http://en.wikipedia.org/wiki/Snell's_law

*April 11, 2013*

**Physics**

a=v/t=20/25 = ...

*April 11, 2013*

**physics**

Please see the Related Questions below

*April 11, 2013*

**Physics**

n=actual depth/apparent depth = =3/(3-1.1) = 3/1.9=1.58

*April 10, 2013*

**physics**

P=(m₁+m₂)g/A=(40+12) •9.8/2(6•4)•10⁻⁴=106167 Pa= 106.167 kPa

*April 10, 2013*

**physics**

v(ave) =total distance/ time taken = =(210+470+150)/(25+20+30) = 11.7 m/s

*April 10, 2013*