Wednesday
March 4, 2015

Posts by Elena


Total # Posts: 4,364

Physics
index of refraction = c/v=λ(vac)/λ(substance) λ(water) =λ(air)/n=650 nm/1.33=489 nm. This is the wavelength of violet light The swimmer sees the red-orange color since our eyes detect the frequency of the light
December 8, 2012

Physics
In vacuum v(red)=v(blue)=v(green)= c=3 x10^8 m/s In glass v(red)>v(green)>v(blue)
December 8, 2012

Physics
F =G•m1•m2/R² the gravitational constant G =6.67•10⁻¹¹ N•m²/kg²,
December 8, 2012

Physics
Yes F =G•m1•m2/R² the gravitational constant G =6.67•10⁻¹¹ N•m²/kg² (!!!!)
December 8, 2012

Physics
(a) mv²/2=W(fr) =F(fr)s=μNs=μmgs s= mv²/2μmg= v²/2μg s is the same for the both cars (b) s↑ since μ↓
December 8, 2012

Physics
(a) using dynamics mgh=mv²/2 v=sqrt(2gh) (b) using kinenatics h=gt²/2 =>sqrt(2h/g) v=gt=gsqrt(2h/g)=sqrt(2gh)
December 8, 2012

science
L=10 cm, E= 200 GPa=200•10⁹ Pa σ=F/A =350 MPa =350•10⁶ Pa ε= ΔL/L Hook's law E= σ=E•ε=E•ΔL/L, ΔL= σ•L/ E =350•10⁶•10/200•10⁹ =0.0175 cm
December 8, 2012

Physics
L=0.2 m (a) mg=kx₁ L₁=L+ x₁=L+ (mg/k)=… (b) m•sqrt(g²+a²)=kx₂ L₂=L+x₂= L + m•sqrt(g²+a²)/k = …
December 8, 2012

physics
The roentgen is the quantity of radiation which liberates by ionisation 1 esu of electricity per 1 cm³ of air under normal conditions of temperature and pressure 1 electrostatic unit of charge (esu) = 3.33•10⁻¹º C 150 mR/hr =150•10⁻³/...
December 8, 2012

physics
V=60 cm³ 500 mR/min= 500•10⁻³/60 = 8.33•10⁻³ R/s, the charge in 1 cm³ is q= 8.33•10⁻³•3.33•10⁻¹º =2.78•10⁻¹² C in chamber Q=2.78•10⁻¹²•60 =1.67&#...
December 8, 2012

Physics
The alcohol in the first arm floats on top of the denser glycerin and pressures it down distance h from the initial level. As a result, the glycerin rises by the distance h in the second arm. Due to the equilibrium condition, the point of the two liquids contact in the 1st arm...
December 7, 2012

Physics
Use T=2π•sqrt(L/g)
December 7, 2012

Physics, check my answer pls
Ans: C
December 6, 2012

Physics
F =G•m1•m2/R² the gravitational constant G =6.67•10⁻¹¹ N•m²/kg²,
December 6, 2012

Science ~conversions~
a= F/m=0.001/1.5•10⁻³=0.67 m/s²
December 5, 2012

Math 310 Math for Teachers
v(X)=v1 v(Y) = v2 s is the distance between A and B t is the time before the 1st meeting v1•t=120, v2•t=s-120, {(s-120)+(s-90)} =v1•6, v2•6=120+90. => v2=(120+90)/6=210/6=35 mph ----- t=120/v1 (1) 2s-210=6•v1 (2) 35•t=s-120 (3) === Substitute...
December 5, 2012

physics
m₁v₁²/2 =qU => v₁ =sqrt(2qU/m₁) m₂v₂²/2 =qU => v₂=sqrt(2qU/m₂) v₁/v₂=sqrt(2qU/m₁)/sqrt(2qU/m₂)=sqrt(m₂/m₁) in magnetic field: ma=qvBsinα a=v²/R, α=90°, sin90...
December 5, 2012

Science
Radioactive decay law N =N₀exp(-λt)= =N₀exp(-ln2•t/T)= =20exp(-0.693•18000/6000) = 2.5 g
December 5, 2012

Physics
KE=mv²/2 = (mv)²/2m =p²/2m p=sqrt(2m•KE) = ... p=mv => v=p/m=...
December 5, 2012

Physics
Units????
December 5, 2012

pHYSICS
water: Q=cmΔT=4180•0.063•(49.7-21.2)=7505.19 J=1792.6 cal peanut: 0.59 g (or kg???) calorie content = 7505.19/0.59•10⁻³ J/kg=1792.6 /0.59•10⁻³ cal/kg =
December 5, 2012

Physics
Δt=1min/110=60/110=0.55 s FΔt=Δp= mΔv= m[v-(-v)] =2mv F=2mv/Δt =2•0.008•550/0.55 =16 N
December 5, 2012

Phyiscs
The height of the first stone is h₀=v₀²/2g=27²/2•9.8 = 37.2 m. v=v₀-gt, v=0 => the time of the upward motion is t= v₀/g =27/9.8=2.8 s. The 1st stone was falling down during t₁=5.5-2.8 = 2.7 s, when the 2nd stone started. The 1st ...
December 5, 2012

physic
v=200 km/h, v₀= 70 km/h, Angle that make v and v₀ is 45° => An angle α in cosine law is α (360°-2•45°)/2 =135° Cosine law: V=sqrt(v²+v₀²-2vv₀cos α)= =sqrt[40000+4900-2•200•70•(-0.707)]=254 ...
December 5, 2012

Physic
A₁v₁=A₂v₂ (πd₁²/4)v₁=(πd₂²/4)v₂ v₂=(d₁²/d₂²)v₁=(16d₁²/d₁²)1 m/s=16 m/s
December 5, 2012

Physics
F=ma a=F/m v=sqrt(2as)
December 5, 2012

Physics
a=F/(m1+m2+m3)
December 5, 2012

Physics
mgh=mv₀²/2 v₀=sqrt(2gh)=sqrt(2•9.8•10.4)=14.28 m/s v= v₀-at, v=0 => a= v₀/t = 14.28/3.58 =4 m/s² F=ma=68.2•4=272.8 N
December 5, 2012

Physics- PLEASE HELP
v =331sqrt(T/273) v1=331sqrt(300/273) =347 m/s v2=331sqrt(313/273) =354 m/s Fundamental frequency λ=4L f=v/ λ => f1/f2 =v2/v1 => f2=f1(v2/v1)=715(354/347)=729 Hz f(beat) =f2-f1= 729-715 =14 Hz
December 5, 2012

physics
v=ω•R=2π•n•R =2π•(1800/60) •0.26=… a(centripetal) = v²/R=…
December 3, 2012

Physics- Elena please help!
Mass per unit length m(o) =0.011 kg/m T=46 N Speed in the stretched string is v = sqrt(T/m(o)) =sqrt(46/0.011)= 64.7 m/s λ=2L=1.2 m f=v/ λ=64.7/1.2=53.9 Hz Resonant frequency F(n)=n•v/2L=n(64.7/1.2)=53.9•n=20000 n=20000/53.9 =370 => f(n)= n•v/2L=...
December 3, 2012

Physics
F=F(fr)=μN=μmg
December 3, 2012

Physics- Someone Please Help!!!
Mass per unit length m(o) =0.011 kg/m T=46 N Speed in the stretched string is v = sqrt(T/m(o)) =sqrt(46/0.011)= 64.7 m/s λ=2L=1.2 m f=v/ λ=64.7/1.2=53.9 Hz Resonant frequency F(n)=n•v/2L=n(64.7/1.2)=53.9•n=20000 n=20000/53.9 =370 => f(n)= n•v/2L=370...
December 3, 2012

Physics URGENT!!!
f(n) = nv/2L The lowest frequency is f1=v/2L =343/2•0.306=560 Hz. Distance between adjacent antinodes is λ/2 and λ=v/f So λ2=v/2f=343/2•41000 =0.0042 m
December 3, 2012

Physics
Average speed= total distance /time taken= = 3200/13.5•60 =3.95 m/s Average velocity = total displacement/time taken = 0.
December 3, 2012

physics
F =G•m1•m2/R² the gravitational constant G =6.67•10⁻¹¹ N•m²/kg²,
December 3, 2012

Physics
b. emitted electrons are more energetic Einstein's relation for phptoelectric effect: hc/λ=v W= KE, λ↓ KE↑
December 3, 2012

Physics!!!
y=3.17cos38.6 =3.17 •0.78=2.48 h= 3.17 - 2.48=0.69 v=3.68 m/s
December 2, 2012

physics
KE=mv²/2 v=sqrt(2KE/m)
December 1, 2012

Physics HW Help, Please
E= mv²/2
December 1, 2012

physics
Pascal’s principle F1/A1=F2/A2. F(bc)={A(bc)/A(mc)}•F(pedal) = =(1.83/6.32) •49 =14.2 N This is the normal force exerted on the brake shoe. The frictional force is F(fr) =μ F(bc)=0.442•14.2 =6.3 N
November 30, 2012

PHYSICS - PLEASE HELP
W=m•g•h=m•g•d•sin30
November 30, 2012

PHYSICS - PLEASE HELP
W=m•g•h=m•gvdvsin30
November 30, 2012

Physics
U =mgh-mv²/2
November 30, 2012

Physics
by 4
November 30, 2012

PHYSICS - PLEASE HELP
(A) KE₁=m₁v₁²/2= (m₁v₁)²/2 m₁=p₁²/2m₁ KE₂=m₂v₂²/2= (m₂v₂)²/2 m₂= p₂²/2m₂ KE₁=KE₂ p₁²/2m₁=p₂²/2m₂ p₁...
November 30, 2012

physics
Δy=Lλ/d = 1•500•10⁻⁹/0.001=…
November 30, 2012

physics
ΔPE=m•g•h=m•g•s•sinα
November 30, 2012

physics
ΔKE=ΔPE +W(fr)= m•g•s•sinα+μ•m•g•s•cosα= =m•g•s(sinα+μ•cosα)
November 29, 2012

Physics
v⒳=v₀•cosα v⒴=v₀•sinα L=vₒ²•sin2α/g, h= vₒ²•sin²α/2g, t= 2vₒ•sinα/g
November 29, 2012

physics
mgh₁=mv₁²/2 mgh₂=mv₂²/2= m(3.9v₁)²/2=15.21 mv₁²/2 h₂=15.21h₁
November 29, 2012

Physics, Please Help
F =G•m1•m2/R² the gravitational constant G =6.67•10⁻¹¹ N•m²/kg², R=h+R(Earth)= (455+6370)•10³ m
November 29, 2012

PHYSICS PLEASE HELP ME
The law of conservation of linear momentum vector p₁ +vector p₂ =vectorp₁`+vector p₂` Projections on the axis x and y p₁⒳ +p₂⒳= p₁`⒳+p₂`⒳ p₁⒴ +p₂⒴= p₁`⒴+p₂`⒴...
November 29, 2012

science
stratovolcano
November 29, 2012

physics
p₁+ρ‧ν₁²/2 +ρ‧g‧h₁ = p₂+ρ‧ν₂²/2 +ρ‧g‧h₂ p₁ = p₂+ρ(ν₂²-ν₁²)/2 +ρ‧g(h₂-h₁)= =141855 +1354‧...
November 29, 2012

physics
(a) continuity equation: A₁v₁=A₂v₂ π‧d₁²/4‧v₁=π‧d₂²/4‧v₂ v₂=v₁(d₁/d₂)² =82.4 m/s. (b) p₁=1.4 atm = 141855 Pa h₂-h₁ =-7.82 m Bernoulli ...
November 29, 2012

Physics
a=F/m
November 29, 2012

Physics
F=k•q1•q2/r² k =9•10^9 N•m²/C²
November 29, 2012

math
Write the expression thrice the sum of m and 8
November 27, 2012

Physics
Units????????
November 27, 2012

Physics
F(total) =4748 -3969 =779 (directed to the east) Win – Theta Chi It’s better to pull straight on
November 27, 2012

physics
The pressure at the depth d p1= ρ•g•d + p (atm) =1024•9.8•18.9 + 101325 =2.91•10 ⁵ Pa, The pressure at the height h p=p₀exp{-μgh/RT) Since we don’t know the temperature, we use another expression. Air pressure above sea level...
November 27, 2012

Physics
sinα=1/20=0.05 sinα=h/s => h=s•sinα W=ΔPE=m•g•h=(m₁+m₂)•g•s•sinα=..
November 27, 2012

physics
m₁=1500 kg, m₂=2500 kg, v₁=5mph=2.24 m/s, claimed velocity is u=10 mph=4.47 m/s, real speed of the pickup is v₂=? μ=0.49, s=5 m. Law of conservation of linear momentum m₁•v₁+m₂•v₂=(m₁+m₂)•v, law of...
November 26, 2012

Physics
m=2.5 kg. R=D/2=0.1 m, n₀=3600 rpm=3600/60=60 rev/s t=10 s. F=? 2πn=2πn₀-εt. Final n=0 2πn₀ = εt. ε =2πn₀/t. Newton’s 2 law for rotation: Iε=M. If the wheel is disc I=mR²/2, M=FR. Then (mR²/2) •...
November 26, 2012

Physics
Tuning fork has frequancy f= 200 Hz +> it makes 200 oscollations during 1 s. Since 1 min=60 s, it makes 200•60=12000 oscillations/min. Each oscillation = 4A=4•0.13 cm=4•0.0013 m=0.0052 m. Therefore, s=0.0052•12000=62.4 m.
November 26, 2012

physics
Ampere’s force F=ILBsinα F(ℓ)=F/L=IBsinα=7.5•0.7•sin45 = ...
November 26, 2012

Physics
F(fr)=μN=μmg=0.032 •55.2•9.8=....
November 26, 2012

physics
Δp=(m1+m2)Δν=(66+7.1)(9.4-6.5)=202 kg•m/s
November 26, 2012

Physics
t= 2vₒ•sinα/g
November 26, 2012

physics
h=gt²/2 t=sqrt(2h/g) L=v•t=36•sqrt(2•162/9.8)=… v(x)= 36 m/s v(y)=gt=g•sqrt(2h/g)=...
November 26, 2012

physics
T=2•π•sqrt(m/k) Solve for ’m’
November 26, 2012

physics ..PLEASE HELP ASSIGN DUE SOON :(
http://answers.yahoo.com/question/index?qid=20121124093302AA02rcf
November 26, 2012

physics
T=2π•sqrt(L/g) g=3.7 m/s² Solve for ‘L’
November 26, 2012

physics
T=2π•sqrt(L/g) g=9.8 m/s² Solve for ‘L’
November 26, 2012

Physics
Flows to the Earth ΔS(E)=6000/295 =20.34 J/K Flows out of the Sun ΔS(S)=-6000/5650 =- 1.062 J/K ΔS= ΔS(E)+ ΔS(S)= 20.34 -1.062= 19.278 J/K
November 26, 2012

Physics
Q=r•m ΔS=Q/T₀=r•m/T₀=333•10⁵•0.0951/273=1.16•10⁴ J/K If environment temperature is T, ΔS= - Q/T= - 333•10⁵•0.0951/T= …
November 26, 2012

Physics
m = W•T1/(T1-T2)• r =...
November 26, 2012

Physics
T1=273+170=443 K T2=273+23=296 K efficiency =(Q1-Q2)/Q1 =W/Q1 efficiency =(T1-T2)/T1 W/Q1 = (T1-T2)/T1 Q1=W•T1/(T1-T2) Q1= r•m r= 333•10⁵ J/kg W•T1/(T1-T2) =r•m r= W•T1/(T1-T2)•m=...
November 26, 2012

Physics
W=1,300 J Q2=6,100 J Q1 =? W=Q1-Q2 Q1=W+Q2 efficiency =(Q1-Q2)/Q1 =W/Q1
November 26, 2012

Physics
W= - p•ΔV = -0.8•(-5)•10⁻³•1.013•10⁵ = =405.2 J ΔU =Q+W=-380+405.2=252 J
November 26, 2012

Physics
(a) Ti=273+7.4=280.4 K Vi/Ti = Vf/Tf Vi/280.4 =8 Vi/Tf Tf=8•280.4 = 2243.2 K b) p•ΔV=νRΔT ν =1 mol p•ΔV= RΔT W = p•ΔV= RΔT= = 8.31•(2243.2-280.4)= =1.63•10⁴ J =16.3 kJ
November 26, 2012

physics
When the cart is 14 cm from the left end of the track, it has a displacement of x=14 -11 cm =3 cm= 0.03 m from the equilibrium position. The speed of the cart at this distance from equilibrium is v=sqrt{k(A²-x²)m}=…
November 26, 2012

The Binding Energy of Electrons?
Energy of photon: E = hc/λ h = Planck’s constant = 6.626•10⁻³⁴ J•s = 4.14•10⁻¹⁵ eV•s c = speed of light = 3•10⁸ m/s λ = wavelength = 0.954 nm = 0.954•10⁻⁹m E = 4.14•10⁻...
November 26, 2012

physics
A=4.2 cm = 0.045 m. v(max) =Aω=A•sqrt(k/m)=...
November 26, 2012

physics
T=2•π•sqrt(m/k)= 2•π•sqrt(0.223/10.20)= …
November 26, 2012

Physics
Flows to the Earth ΔS(E)=6000/295 =20.34 J/K Flows out of the Sun ΔS(S)=-6000/5650 =- 1.062 J/K ΔS= ΔS(E)+ ΔS(S)= 20.34 -1.062= 19.278 J/K
November 26, 2012

PHYSICS - PLEASE HELP
mv=MV M=mv/V=9.6•0.53/0.12=42.4 kg
November 26, 2012

Physics
Mv²/2 =4mcΔT ΔT = Mv²/8mc=1750•28²/8•8•448=47.9℃
November 26, 2012

PHYSICS
KE=mv²/2 ½KE=mcΔT ΔT= KE/2mc= mv²/4mc= = v²/4c=390²/4•130=292.5℃
November 26, 2012

Physics Can you help me get started
http://answers.yahoo.com/question/index?qid=20100629105308AAL8TBp
November 26, 2012

Physics
p=mv=2.3•10⁶•6•10⁶=13.8•10¹² kg•m/s. p₁= m₁v₁= 5.2•10⁵•2•10⁶=10.4•10¹¹kg•m/s. p₂=m₂v₂=8.4•10⁵•9•10 ⁵=75.6•10¹...
November 26, 2012

PHYSICS
For water, density is ρ =1000 kg/m ³, V =4•10¹¹ m³ => m=ρ•V=1000•4•10¹¹ =4•10¹⁴ kg, c =4183 J/kg•K, ΔT=11-9 =2 K. E=Q= m•c• (T₁-T)= m•c• ΔT =4•10¹...
November 26, 2012

PHYSICS
mgh=mv²/2 mv²/2=mcΔT => mgh=mcΔT gh=cΔT c =4183 J/kg•K, ΔT=gh/c=9.8•807/4183 =1.9° T1=T+ ΔT=16.7+1.9=18.6℃
November 26, 2012

Physics
Cu: m₁=0.1 kg, c₁=385 J/kg•K, T₁=460 K, Al: m₂=0.2 kg, c₂=930 J/kg•K, T₂=220 K, Water: m₃=0.5 kg, c₃=4183 J/kg•K, T₃280 K. T=? m₁c₁(T₁-T) = m₂c₂(T-T₂) +m₃c₃(T-T...
November 26, 2012

optics
http://www.optiboard.com/forums/showthread.php/18768-Need-Help-For-Ophthalmic-Question! and page 30 from http://www.optometry.co.uk/uploads/articles/949e0d09ac024c2edb6d55bad5da4d11_jalie20050225.pdf
November 26, 2012

physics
k = 1080 N/m, r = 0.0143 m, A = πr²= π•0.0143²=6.42•10⁻⁴ m² The pressure P = F/A = ρ•g•h, where water density is ρ = 1000 kg/m³ g = 9.8 m/s² , x = 0.0075 m For the elastic force of the spring F = kx. ...
November 26, 2012

physics/optics
Try this http://www.opticampus.com/files/introduction_to_ophthalmic_optics.pdf
November 26, 2012

physics
¹⁵₈O + ₋₁⁰e=¹⁵₇N
November 26, 2012

Physics
0=v-at a=v/t F=ma=mv/t (a) F₁ =m•v/t₁= =60.8•5.31/4.52•10⁻³=71426.5 N (b) F₂=m•v/t₂ = =60.8•5.31/0.209 = 1544.7 N. (c) mg=60.8•9.8=595.8 N ground force: F=F₁+mg=71426.5+595.8=72022.3 N F=F₂+mg=1544.7+...
November 26, 2012

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