# Posts by Elena

Total # Posts: 4,389

**physics**

PE=kx²/2 k=2•PE/ x²= =2•2.5/0.15²=222 N/m

*December 12, 2012*

**physics**

PE =KE =KE(trans)+ KE(rot) = mgL=mv²/2 +Iω²/2= =m ω²L²/2 + m ω²L²/3•2= =2 m ω²L²/3, ω=sqrt(3g/2L)=sqrt(3•9.8/2•1.2) = =sqrt(12.24)=3.5 rad/s

*December 12, 2012*

**physics**

mg= F =G•m •M/(R+h)² g= G•M/(R+h)² the gravitational constant G =6.67•10⁻¹¹ N•m²/kg², h=3600000 m=3.6•10⁶ m Earth’s mass is M = 5.97•10²⁴kg, Earth’s radius is R = 6.378•10&#...

*December 12, 2012*

**Physics**

F(fr)=μ•N=μ•m•g•cosα

*December 11, 2012*

**Physics**

F(fr)=μ•N=μ•m•g μ=F(fr)/mg

*December 11, 2012*

**Science**

The most common mineral of the Earth's continents is quartz, the mineral SiO2.

*December 11, 2012*

**science**

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

*December 11, 2012*

**science**

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

*December 11, 2012*

**science**

http://www.chem4kids.com/files/elem_pertable.html http://en.wikipedia.org/wiki/Periodic_table

*December 11, 2012*

**science**

http://www.chem4kids.com/files/atom_bonds.html

*December 11, 2012*

**Science**

http://www.chem4kids.com/files/atom_electron.html

*December 11, 2012*

**physics**

μ=0.14, s=30 m=160 kg x: m•a= m•g•sinα - F(fr), y: 0= - m•g•cosα +N. F(fr)=μ•N= μ• m•g•cosα m•a= m•g•sinα - μ• m•g•cosα a= g(sinα - μ•cosα...

*December 11, 2012*

**English**

we are learning about the 14 tenses: past,present,future,past perfect,present perfect, future perfect, past progressive..., past perfect progressive..., emphatic..and then there is another one but i forgot what that one was. Anyway, i need a website that can help me with these...

*December 10, 2012*

**Math**

Christine currently has $5000 in her 401(k) and plans to contribute $100 each month for the next 30 years into it. What will be the value of Christine's 402(k) in 30 years if the per annum rate of return is assumed to be 12% compounded monthly?

*December 10, 2012*

**English**

We are working on Passive and Active voice. i really don't understand it, so do you know any websites that could help me with passive and active voice.

*December 10, 2012*

**math**

i typed it in my calculator and i got : 1910 but i don't know if that's right? sorry

*December 10, 2012*

**Math**

Christine currently has $5000 in her 401(k) and plans to contribute $100 each month for the next 30 years into it. What will be the value of Christine's 402(k) in 30 years if the per annum rate of return is assumed to be 12% compounded monthly?

*December 10, 2012*

**physics**

weight = mg

*December 10, 2012*

**physics**

2.5x/25 = x/do do=25x/2.5x=10cm 1/di+1/do=1/f 1/25 + 1/10 =1/f 7/50=1/f f=50/7=7.14 cm

*December 9, 2012*

**Physics**

N=mgcosα F(fr)= μN = μmgcosα ma=F(fr)+mgsinα => ma= μmgcosα + mgsinα a=g(μcosα+sinα)=.... s=v²/2a=....

*December 8, 2012*

**Physics**

N=mgcosα ma=T-mgsinα => T=m(a+gsinα)

*December 8, 2012*

**physics please help!**

http://www.physics.utoronto.ca/~poptor/solutions05/pss4_optics.pdf

*December 8, 2012*

**Physics**

B.Electric field? A.Magnetic

*December 8, 2012*

**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*