Friday
December 9, 2016

# Posts by Elena

Total # Posts: 4,386

http://m.teachastronomy.com/astropedia/article/Critical-Density
May 21, 2013

In vector form: Δp⃗ =p₂⃗-p₁⃗ =mv₂⃗-mv₁⃗, for magnitudes Δp =p₂-(-p₁) =mv₂+mv₁= 2mv. p=Mu => Mu=2mv The speed of the center of the door is u=2mv/M=2•0.4•35/15 = 1.37 m/s Its ...
May 21, 2013

Physics
The angular momentum of the door ‘p’= the change in amgular momentum of the ball Δp. In vector form: Δp⃗ =p₂⃗-p₁⃗ =mv₂⃗-mv₁⃗, for magnitudes Δp =p₂-(-p₁) =mv₂+mv₁= 2mv. p=Mu...
May 21, 2013

Physics
http://www.jiskha.com/display.cgi?id=1368801920
May 21, 2013

physics
p=W/A =W/a²=75/0.01=7500 Pa
May 21, 2013

physics
N=mg => m=N/g = 95/9.8 =9.69 kg
May 21, 2013

physics
s₁=v²/2a₁=28.8²/2•4=103.7 m. s₁=a₁t₁²/2 => t₁=sqrt(2s₁/a₁) =sqrt(2•103.7/4) =7.2 s. t₂=63.8 s. s₃=v²/2a₃=28.8²/2•1.58=262.5 m s₃=a₃t₃²/2 => t...
May 21, 2013

physics
s=at²/2=100•25/2=1250 m
May 21, 2013

PHYSICE
http://teacher.pas.rochester.edu/phy121/lecturenotes/Chapter13/Chapter13.html
May 21, 2013

physical science
ΔKE =Work mv₂²/2 - mv₁²/2 = W v₂= sqrt{(2/m)•[W+ mv₁²/2]}=…
May 20, 2013

physics
a=eE/m s=v²/2a
May 20, 2013

Physics
t=sqrt{2h/g} v=L/t
May 18, 2013

physics
φ=31⁰π/180⁰ = 0.54 rad. n = 900 rev/min =900/60 =15 rev/s t=φ/ω= φ/2πn=0.54/2π•15=0.006 s v=d/t =0.8/0.006 = 133 m/s
May 18, 2013

physics
See my answer to a similar question below under related questions.
May 18, 2013

Physics
t=sqrt{2h/g}
May 17, 2013

physics
D) {4•100 +4•80} – sqrt(400² +80²) = 72 m
May 17, 2013

physics
Upward motion: h=v₀t-gt²/2 v= v₀-gt v=0 => t=v₀/g h= v²/2g =30²/2•9.8=45.9 m t=sqrt{2h/g} =sqrt{2•45.9/9.8} = 3.06 s. t(total)=2•t = 2•3.06 =6.12 s.
May 17, 2013

science-physics
W•0.67 = 183•(1.4-0.67) +107•(2.8-0.67) W={183•0.73+107•2.13}/0.67=540 N
May 15, 2013

Physics
λ =v/f=330/320 = ... m
May 15, 2013

physics
Velocity in the stretched string is v = sqrt(TL₀/m) = =sqrt(570•0.92/0.0037) = 376 m/s, λ =2L =2•0.65 = 1.3 m, λ = v/f => f=v/λ =376/1.3=289 Hz.
May 14, 2013

Physics
mgh = mv²/2 v=sqrt{2gh}
May 14, 2013

Physics helpp
F-F(gr) = ma a= {F-F(gr)}/m = =(15-10)/15=0.33 m/s² (upward)
May 14, 2013

science physics
1,2). k =9•10⁹ N•m²/C², q₁=5 C, q₂= - 2.5 C. F=k•q₁•|q₂|)/r² = =9•10⁹•5•2.5/1.75² =3.67•10¹⁰ N (to the right). 3). E=k|q₂|/r² =9•10⁹•2.5/1.75&#...
May 14, 2013

physics
k =9•10⁹ N•m²/C² F=k•q₁•q₂/r² = =9•10⁹•5•2.5/1.75² =3.67•10¹⁰ N (to the right)
May 14, 2013

physical science
a=F/m = 14000/2500 =5.6 m/s^2
May 14, 2013

Physics
m=14 kg F=ma=14 x 1.5 = 21 N
May 14, 2013

Physics to Elena
(a) The time-averaged Poynting vector is <S> =cε₀E₀²/2. The amplitude of electric field is E=sqrt{2<S>/ cε₀} = =sqrt{2•1.35•10³/3•10⁸•8.85•10⁻¹²} = 1.01•10³ V/m. (b) The ...
May 14, 2013

Physical Science
KE=mv²/2 m= ρV kinetic energy per unit volume V KE₁ =KE/V= mv²/2V =ρV•v²/2V = ρv²/2
May 13, 2013

Physical Science
KE=ρv²/2= 1•10³•0.5²/2=125 J
May 13, 2013

physics
Coulomb’s Law: F=k•q₁•q₂/r² =… F=ma => a=F/m=… r=at²/2 t=sqrt{2r/a)=…
May 13, 2013

physics
F(BC) =kq²/a² q´(B)=q´(A) =(q+0)/2=q/2, q´´(A) =q´(C) = {q´(A)+c(C)}/2 = 3q/4 F´(BC) =k q´(B)• q´(C)/a² = =(3/8)• kq²/ a²=3•4/8=3.2 = 1.5 N
May 13, 2013

physics/chemistry(kinetic ..gasses)
<v> =sqrt{3RT/M}=sqrt{3pV/m} => M=mRT/pV =ρRT/p. v=sqrt {γRT/M}. γ=C_p /C_v = (i+2)/i. v=sqrt{9i+2)RT/iM} = sqrt{(i+2)RTp/iρRT}= =sqrt{(i+2)p/iρ}, iρv² - ip = 2p, i=2p/ (ρv² - p) = =2• 1.01325• 10⁵/(1.3&#...
May 13, 2013

Physical Education
mg=F(buoyant), ρ₁Vg=ρ₂0.64Vg, ρ₁=0.64ρ₂=0.64•806=515.84 kg/m³.
May 13, 2013

physics
F(BC) =kq²/a². q´(B)=q´(A) =(q+0)/2=q/2, q´´(A) =q´(C) = {q´(A)+c(C)}/2 = 3q/4, F´(BC) =k q´(B)• q´(C)/a² = =(3/8)• kq²/ a²=3•4/8=3.2 = 1.5 N
May 12, 2013

physics
s=v•t=...
May 12, 2013

Physics
eU=mv²/2 v=sqrt{2eU/m} = sqrt{2•1.6•10⁻¹⁹ •750/5.2•10⁻²⁷) =6.7•10⁴ m/s mv²/R=evB R=mv/eB =5.2•10⁻²⁷•6.7•10⁴/1.6•10⁻¹⁹•0.65 = 3.4•10...
May 11, 2013

Physics
F=ma=evBsinα a= evBsinα/m =1.6•10⁻¹⁹•7.5•10⁶•0.04•sin50/9.1•10⁻³¹= 4•10¹⁶ m/s²
May 11, 2013

physics
A=0.1 m ω=sqrt(k/m) =sqrt(100/4) =5 rad/s v(max) =Aω =0.1•5=0.5 m/s
May 11, 2013

ThermoPhysics
Adiabatic index γ=(i+2)/i=(5+2)/5= 1.4. (a) p₁(V₁)^γ=p₂(V₂)^γ V₁/V₂ =( p₂/p₁)^(1/ γ)=20.5^(1/1.4)= =20.5^(0.714)=8.65. (b) (p₂/p₁)^(γ-1) = (T₂/T₁)^γ (T₂/T₁) =((p&#...
May 11, 2013

Physics
a=v²/2s=... s=at²/2 => t=sqrt{2s/a)=...
May 11, 2013

Physics
I=8.28•10⁻³⁸ g•cm²=8.28•10⁻⁴⁵kg•m², I=2mr²/3 => radius of diatomic molecule r=sqrt{3•I/2m} Root mean square speed v =sqrt{3kT/m}. v = ωr. Angular root mean square speed ω=v/r= =sqrt{2kT/I...
May 10, 2013

Physics: Manitude of Surface Charge on Dielectric
If the electric susceptibility κ=4.5, electric permittivity is ε = κ+1 = 5.5 C₁=q₁/V, q₁=C₁V=1.86•10⁻⁶•12=2.23•10⁻⁵ C, C₁=ε₀A/d = q₁/V, C₂=εε₀A/d = q&#...
May 10, 2013

Physics: Capacitance of Capacitor
Q₁=Lf•m = C₁V²/2 Q₂=Lv•m = C₂V²/2 Lf•m/ Lv•m=2C₁V²/2 C₂V² C₂=Lv•C₁/Lf = 22.6•10⁵•8/33.5•10⁴= 53.97 μF
May 10, 2013

Physics: Potential Difference
C₂=kC₁ Energy = CV²/2 C₁V₁²/2=C₂V₂²/2 V₂=V₁/√(k)=15/√(3.6) = 7.9 V
May 10, 2013

Physics: Dielectric Constant
C=εε₀A/d ε=Cd/ε₀A = =9.1•10⁻⁶•1.5•10⁻⁵/8.85•10⁻¹²•2 =7.7.
May 10, 2013

la porte high school
h= gt²/2, t=2h/g=2•12/9.8=2.45 s s=v•t = 15•t=15•2.45 = 36.7 m
May 10, 2013

physical
m=ρV=ρπr²h=1950•π•0.051²•0.003=0.048 kg
May 10, 2013

physics
The law of conservation of linear momentum m₁v₁- m₂v₂=(m₁+m₂)u u={m₁v₁- m₂v₂}/(m₁+m₂)
May 10, 2013

physics
F=kx k=F/x W=ΔPE= kx²/2=Fx²/2x= Fx/2=20•0.05/2=0.5 J
May 10, 2013

Physics
F=0 if E = 0 The point is located to the right from the second charge at the distance ‘x’ => kq₁/(X+x)² =kq₂/x² X=1 64/(1+x)² = 16/ x², 3x²-2x-1 =0 , x={2±sqrt(4+12)}/6. x₁=1, x₂=-1/3 (※) Ans: ...
May 9, 2013

physics
Use Right Hand Rule
May 9, 2013

physics
30 = L/v(s) - L/v(p) = =2L/v(p) - L/v(p) = L/v(p), L=30 v(p) = 30•6000=180000 m=180 km
May 9, 2013

physics
1/R +1/R =1/9 2/R =1/9 R=18 Ω
May 9, 2013

physics
R₁=R/4 1/R₀=4/R₁ R₀=R₁/4= R/4•4= R/16
May 9, 2013

physics
I can't understand your given data
May 9, 2013

physics
R₁=R/4 1/R₀=4/R₁ R₀=R₁/4= R/4•4= R/16
May 9, 2013

physical scinsce
F=1000n, F=ma, a=F/m=1000n/10= 100n. a=v²/2s, v²/2s=100n, n= v²/200s=50²/200•10=1.25. The amount of explosive is 1.25•10 =12.5 kg.
May 9, 2013

physics
F=qvBsinα sinα = sin180= 0 => F=0
May 9, 2013

physics
incandescent solids produce a continious spectrum of radistion, excited gases - line spectrum
May 8, 2013

Physics
This is correct solution
May 8, 2013

Physics
ma= Fcos θ –μ(mg-Fsin θ) μ = (Fcos θ -ma)/ (mg-Fsin θ)
May 8, 2013

physics
T=2π•sqrt(L/g) = 2π•sqrt(1.8/3.69) =4.4 s
May 8, 2013

Number of nuclei N=n•N(A) = (m/μ) • N(A)= =(3 g)•(6.022•10²³ nuclei/mol)/(63 g/mol)=2.87•10²² nuclei The energy required to break all the copper nuclei into their constituent protons and neutrons is (550 MeV ) •(2.87•...
May 8, 2013

¹₀n+¹º₅B = ⁷₃Li+⁴₂He Δm = m(¹₀n) + m(¹º₅B) – m(⁷₃Li)-m(⁴₂He)= =1.009 + 10.811 – 6.941 – 4.003 = 0.876 u. ΔE=mc²=0.876 •1.66•10⁻&#...
May 8, 2013

Physics to Elena
Number of nuclei N=n•N(A) = (m/μ) • N(A)= =(3 g)•(6.022•10²³ nuclei/mol)/(63 g/mol)=2.87•10²² nuclei The energy required to break all the copper nuclei into their constituent protons and neutrons is (550 MeV ) •(2.87•...
May 8, 2013

Physics to Elena
I believe that the correct answer is 1.58•10¹⁴ J.
May 8, 2013

Physics!
Activity A = λN =ln2•N/T, N=AT/ln2=2.51•10⁵•7.55•10⁶/0.693= =2.73•10¹² nuclei. The mass is m=2.73•10¹²•0.035/6.022•10²³ = =1.6•10⁻¹³ kg
May 8, 2013

v=0.02•3•10⁸=6•10⁶ m/s 1 MegaParsec = 3.26•10⁶ ly Hubble’s Law v=Hd Hubble constant H ~70- 80 km/(s•Mpc) => v= 80d or v=70d d=(6•10⁶/80 000)• 3.26•10⁶ =2.45•10⁸ ly or d=(6•10⁶/...
May 8, 2013

Physics
F=k•q₁•q₂/r² k =8.98755•10⁹ N•m²/C²
May 8, 2013

Physics
Point A: h₁= 22 m, v₁=16 m/s; Point B: h₂= 32 m, r₂= 10 m, v₂=?; Δh₁₂ = h₂-h₁=32-22 = 10 m; Point C: h₃=0, r₃= 20 m, v₃=?; Δh₂₃ = h₂-h₃ = 32 – 0 = 32 m. KE₁+PE...
May 8, 2013

Physics
Number of atoms is N= N(A)•m/μ = =6.022•10²³•0.003/63.5•10⁻³=2.85•10²². Number of nucleons (protons+neutrons) = =2.85•10²²•63=1.8•10²⁴. Energy = 1.8•10²⁴•550&#...
May 7, 2013

The decay constant is λ=ln2/T = 0.693/5730 = 1.209•10⁻⁴ yr⁻¹. The fraction of ¹⁴C << ¹²C, => we use the atomic weight of ¹²C to find the number of carbon atoms in 270 g: N= (270/12)•6.022•10&#...
May 7, 2013

physics
R=ρL/A A=πd²/4
May 7, 2013

physics
ρgh=σ/r r = σ/ ρgh=0.0072/1000•9.8•0.2 = = 3.7•10⁻⁵ m= 37μm
May 6, 2013

Physics
η=W/Q =(T₁-T₂)/T₁=1-(T₂/T₁), T₂=T₁(1 – W/Q)= 301(1- 216/2360)=280.7 K
May 5, 2013

Physics
V=V₀sinωt, ω= ω₀=1/sqrt(LC)=1/sqrt(0.015•5•10⁻⁶)= =3652 rad/s. V(t)=40sin3652t. q=CU, q(t) =CV₀sinωt, q(t) =5•10⁻⁶•40sin3652t=2•10⁻⁴sin3652t, I(t) =dq/dt =d(CV₀sinωt)/...
May 5, 2013

physics
h=(u²- v²)/2g v²=u²- 2gh, KE=m•v²/2= m(u²- 2gh)/2, KE=PE => m(u²- 2gh)/2 =mgh, (u²- 2gh)/2= gh, u²=4gh, h= u²/4g.
May 5, 2013

SCIENCE
http://en.wikipedia.org/wiki/Atmospheric_pressure
May 5, 2013

Physics
F=ILBsinα sinα=sin 90⁰=1 => F=ILB =6600•7.65•1.25 =6.31 •10⁴ N F=ma => a=F/m= 6.31 •10⁴/2940 = 21.5 m/s².
May 4, 2013

Finance
A company has identified the following investments as looking promising. Each requires an initial investment of \$1.2 million. Which is the best investment? a)a perpetuity that generates a cash flow at the end of year 1 of \$100,000, has a growth rate of 1.25%, and a cost of ...
May 4, 2013

Physics 1
λ =2L=2•0.5 = 1 m v= λ•f=1•261.6 = 261.6 m/s v = sqrt(T/m₀)= =sqrt(T•L/m) v²= T•L/m T= v²m/L=261.6²•3.8•10⁻³/0.5=520.10 N
May 3, 2013

physics
α= β => α + β=2 β =120⁰ β=60⁰
May 3, 2013

Physics
v₂=v₁/2, m₂=2m₁. p₁= m₁v₁, p₂=m₂v₂=2m₁•v₁/2= m₁v₁=p₁. KE₁=m₁v₁²/2, KE₂=m₂v₂²/2=2m₁ •v₁²/4•2= m₁v₁...
May 2, 2013

Physics
m₁v =(m₁+m₂)u u= m₁v/(m₁+m₂)=2•22/(2+7)=4.9 m/s
May 2, 2013

Physics
v=gt p=mv=mgt
May 2, 2013

Physics
FΔt=Δp= mΔv
May 2, 2013

Physics
0= MV - mv V=mv/M= 10•420/350 = 12 m/s
May 2, 2013

Physics
KE=PE+W(fr) mv²/2 = mgh +µmgcosα = = mgdsinα +µmgcosα, d= {v²/2 - µ gcosα}/gsinα
May 2, 2013

physics urgent please asnwer it i m begging u
I=j(x)A evB(z) =eE(y) E(y)=vB(z) neAv =j(x)A E(y) = j(x)B(z)/ne Constant of proportionality (Hall coefficient) = 1/ne=m³/C = m³/A•s
May 2, 2013

physics
W=ΔKE =mv₂²/2 - mv₁²/2 =m (v₂²/2 - v₁²/2) m= W/(v₂²/2 - v₁²/2)=…
May 2, 2013

physics
PE = mgh m=PE/gh= 800/6•9.8= 13.61 kg
May 2, 2013

physics
λ=c/f f₁=c/λ₁=3•10⁸/320•10⁻⁹ =9.375•10¹⁴ Hz f₂=c/λ₂=3•10⁸/280•10⁻⁹ =1.071•10¹⁵ Hz
April 30, 2013

Physics
T=273+22=295 K radiant emittance R radiant emittance of the black body R* Stefan-Boltzmann law R*=σT⁴ Stefan-Boltzmann constant σ =5.67•10⁻⁸ W•m⁻²•K⁻⁴ R= =kR*=kσT⁴ E=RAt =kσT⁴At E₁=R...
April 30, 2013

Physics
Q/t=q= k•A•ΔT/Δx ΔT=q•Δx/k•A = = 250•1.7•10⁻³/0.2•1.8=1.18 K
April 30, 2013

Physics
L=ℏ √l(l+1) =√l(l+1)• h/2π l= n-1 => l=0, 1, 2, 3,4. L(max) = √(4•5) • 6.63•10⁻³⁴/2π=4.72•10⁻³⁴ kg•m²/s L(min)= 0
April 30, 2013

Physics Need help plz
The uncertainty in speed Δv = 0.22 m/s Δp•Δx =h/4π Δmv•Δx =h/4π Δv•Δx =h/4πm Δx= h/4π•m •Δv= =6.626•10⁻³⁴/4π•1900•0.22=1.26•10⁻³⁷...
April 30, 2013

Physics
Its incorrect. and you shut up so calles i am awesome
April 30, 2013

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